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 $180.27   3.283%   $186.1883   $186.19   $186.20   $186.20  
  Purchase #2 $146.68   8.378%   $158.9689   $158.97   $158.95   $159.00  
  Purchase #3 $91.92   10.213%   $101.3078   $101.31   $101.30   $101.30  
  Purchase #4 $239.68   9.355%   $262.1021   $262.10   $262.10   $262.10  
  Purchase #5 $41.87   11.358%   $46.6256   $46.63   $46.65   $46.60  
  Purchase #6 $14.62   6.428%   $15.5598   $15.56   $15.55   $15.60  
  Purchase #7 $165.63   3.669%   $171.707   $171.71   $171.70   $171.70  
  7 purchase totals = $880.67       $942.4595   $942.47   $942.45   $942.50