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 $125.77   4.509%   $131.441   $131.44   $131.45   $131.40  
  Purchase #2 $69.41   10.575%   $76.7501   $76.75   $76.75   $76.80  
  Purchase #3 $73.50   12.461%   $82.6588   $82.66   $82.65   $82.70  
  Purchase #4 $205.69   11.845%   $230.054   $230.05   $230.05   $230.10  
  Purchase #5 $99.33   3.651%   $102.9565   $102.96   $102.95   $103.00  
  Purchase #6 $51.98   13.500%   $58.9973   $59.00   $59.00   $59.00  
  Purchase #7 $169.88   3.449%   $175.7392   $175.74   $175.75   $175.70  
  7 purchase totals = $795.56       $858.5969   $858.60   $858.60   $858.70