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 $54.32   5.474%   $57.2935   $57.29   $57.30   $57.30  
  Purchase #2 $244.57   6.860%   $261.3475   $261.35   $261.35   $261.30  
  Purchase #3 $25.37   10.503%   $28.0346   $28.03   $28.05   $28.00  
  Purchase #4 $50.38   3.181%   $51.9826   $51.98   $52.00   $52.00  
  Purchase #5 $69.56   8.855%   $75.7195   $75.72   $75.70   $75.70  
  Purchase #6 $245.77   3.403%   $254.1336   $254.13   $254.15   $254.10  
  Purchase #7 $96.66   6.289%   $102.7389   $102.74   $102.75   $102.70  
  7 purchase totals = $786.63       $831.2502   $831.24   $831.30   $831.10