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 $57.65   8.183%   $62.3675   $62.37   $62.35   $62.40  
  Purchase #2 $59.53   11.396%   $66.314   $66.31   $66.30   $66.30  
  Purchase #3 $142.82   4.595%   $149.3826   $149.38   $149.40   $149.40  
  Purchase #4 $182.27   6.313%   $193.7767   $193.78   $193.80   $193.80  
  Purchase #5 $125.65   12.793%   $141.7244   $141.72   $141.70   $141.70  
  Purchase #6 $98.43   6.409%   $104.7384   $104.74   $104.75   $104.70  
  Purchase #7 $78.88   6.499%   $84.0064   $84.01   $84.00   $84.00  
  7 purchase totals = $745.23       $802.3100   $802.31   $802.30   $802.30