Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.66   10.754%   $274.2934   $274.29   $274.30   $274.30  
  Purchase #2 $197.62   3.845%   $205.2185   $205.22   $205.20   $205.20  
  Purchase #3 $156.92   10.172%   $172.8819   $172.88   $172.90   $172.90  
  Purchase #4 $153.41   11.435%   $170.9524   $170.95   $170.95   $171.00  
  Purchase #5 $176.81   13.737%   $201.0984   $201.10   $201.10   $201.10  
  Purchase #6 $111.94   12.181%   $125.5754   $125.58   $125.60   $125.60  
  Purchase #7 $221.65   6.832%   $236.7931   $236.79   $236.80   $236.80  
  7 purchase totals = $1,266.01       $1,386.8131   $1,386.81   $1,386.85   $1,386.90