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 $104.62   11.447%   $116.5959   $116.60   $116.60   $116.60  
  Purchase #2 $125.29   9.526%   $137.2251   $137.23   $137.25   $137.20  
  Purchase #3 $30.60   5.318%   $32.2273   $32.23   $32.25   $32.20  
  Purchase #4 $234.46   10.874%   $259.9552   $259.96   $259.95   $260.00  
  Purchase #5 $206.99   4.183%   $215.6484   $215.65   $215.65   $215.60  
  Purchase #6 $68.32   10.176%   $75.2722   $75.27   $75.25   $75.30  
  Purchase #7 $31.47   3.663%   $32.6227   $32.62   $32.60   $32.60  
  7 purchase totals = $801.75       $869.5468   $869.56   $869.55   $869.50