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 $119.67   11.660%   $133.6235   $133.62   $133.60   $133.60  
  Purchase #2 $119.53   8.720%   $129.953   $129.95   $129.95   $130.00  
  Purchase #3 $28.99   10.793%   $32.1189   $32.12   $32.10   $32.10  
  Purchase #4 $194.63   7.165%   $208.5752   $208.58   $208.60   $208.60  
  Purchase #5 $201.34   8.190%   $217.8297   $217.83   $217.85   $217.80  
  Purchase #6 $118.94   6.343%   $126.4844   $126.48   $126.50   $126.50  
  Purchase #7 $103.63   12.133%   $116.2034   $116.20   $116.20   $116.20  
  7 purchase totals = $886.73       $964.7881   $964.78   $964.80   $964.80