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 $217.45   13.319%   $246.4122   $246.41   $246.40   $246.40  
  Purchase #2 $58.51   7.278%   $62.7684   $62.77   $62.75   $62.80  
  Purchase #3 $112.73   4.415%   $117.707   $117.71   $117.70   $117.70  
  Purchase #4 $143.28   4.522%   $149.7591   $149.76   $149.75   $149.80  
  Purchase #5 $91.95   12.360%   $103.315   $103.32   $103.30   $103.30  
  Purchase #6 $102.95   5.811%   $108.9324   $108.93   $108.95   $108.90  
  Purchase #7 $165.43   8.849%   $180.0689   $180.07   $180.05   $180.10  
  7 purchase totals = $892.30       $968.9630   $968.97   $968.90   $969.00