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 $76.54   12.763%   $86.3088   $86.31   $86.30   $86.30  
  Purchase #2 $138.32   3.145%   $142.6702   $142.67   $142.65   $142.70  
  Purchase #3 $121.56   13.837%   $138.3803   $138.38   $138.40   $138.40  
  Purchase #4 $188.67   5.841%   $199.6902   $199.69   $199.70   $199.70  
  Purchase #5 $179.27   10.185%   $197.5286   $197.53   $197.55   $197.50  
  Purchase #6 $102.86   9.292%   $112.4178   $112.42   $112.40   $112.40  
  Purchase #7 $72.86   7.725%   $78.4884   $78.49   $78.50   $78.50  
  7 purchase totals = $880.08       $955.4843   $955.49   $955.50   $955.50