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 $84.63   8.849%   $92.1189   $92.12   $92.10   $92.10  
  Purchase #2 $246.94   6.482%   $262.9467   $262.95   $262.95   $262.90  
  Purchase #3 $45.94   4.639%   $48.0712   $48.07   $48.05   $48.10  
  Purchase #4 $14.79   13.485%   $16.7844   $16.78   $16.80   $16.80  
  Purchase #5 $79.41   12.707%   $89.5006   $89.50   $89.50   $89.50  
  Purchase #6 $237.48   12.137%   $266.3029   $266.30   $266.30   $266.30  
  Purchase #7 $158.76   11.141%   $176.4475   $176.45   $176.45   $176.40  
  7 purchase totals = $867.95       $952.1722   $952.17   $952.15   $952.10