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 $32.82   10.266%   $36.1893   $36.19   $36.20   $36.20  
  Purchase #2 $68.99   6.369%   $73.384   $73.38   $73.40   $73.40  
  Purchase #3 $53.91   8.105%   $58.2794   $58.28   $58.30   $58.30  
  Purchase #4 $227.68   13.142%   $257.6017   $257.60   $257.60   $257.60  
  Purchase #5 $5.88   5.228%   $6.1874   $6.19   $6.20   $6.20  
  Purchase #6 $152.40   11.608%   $170.0906   $170.09   $170.10   $170.10  
  Purchase #7 $241.34   4.811%   $252.9509   $252.95   $252.95   $253.00  
  7 purchase totals = $783.02       $854.6833   $854.68   $854.75   $854.80