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 $14.39   12.659%   $16.2116   $16.21   $16.20   $16.20  
  Purchase #2 $174.45   3.615%   $180.7564   $180.76   $180.75   $180.80  
  Purchase #3 $223.39   5.776%   $236.293   $236.29   $236.30   $236.30  
  Purchase #4 $163.59   3.695%   $169.6347   $169.63   $169.65   $169.60  
  Purchase #5 $117.86   6.781%   $125.8521   $125.85   $125.85   $125.90  
  Purchase #6 $65.88   4.738%   $69.0014   $69.00   $69.00   $69.00  
  Purchase #7 $53.88   6.384%   $57.3197   $57.32   $57.30   $57.30  
  7 purchase totals = $813.44       $855.0689   $855.06   $855.05   $855.10