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 $204.29   11.596%   $227.9795   $227.98   $228.00   $228.00  
  Purchase #2 $153.61   10.410%   $169.6008   $169.60   $169.60   $169.60  
  Purchase #3 $204.83   5.341%   $215.77   $215.77   $215.75   $215.80  
  Purchase #4 $54.73   6.800%   $58.4516   $58.45   $58.45   $58.50  
  Purchase #5 $131.34   10.340%   $144.9206   $144.92   $144.90   $144.90  
  Purchase #6 $70.86   5.803%   $74.972   $74.97   $74.95   $75.00  
  Purchase #7 $65.97   7.485%   $70.9079   $70.91   $70.90   $70.90  
  7 purchase totals = $885.63       $962.6024   $962.60   $962.55   $962.70