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 $105.82   12.126%   $118.6517   $118.65   $118.65   $118.70  
  Purchase #2 $233.57   13.775%   $265.7443   $265.74   $265.75   $265.70  
  Purchase #3 $163.46   11.517%   $182.2857   $182.29   $182.30   $182.30  
  Purchase #4 $141.83   11.680%   $158.3957   $158.40   $158.40   $158.40  
  Purchase #5 $140.99   3.857%   $146.428   $146.43   $146.45   $146.40  
  Purchase #6 $109.86   12.566%   $123.665   $123.67   $123.65   $123.70  
  Purchase #7 $209.99   12.753%   $236.77   $236.77   $236.75   $236.80  
  7 purchase totals = $1,105.52       $1,231.9404   $1,231.95   $1,231.95   $1,232.00