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 $61.99   6.454%   $65.9908   $65.99   $66.00   $66.00  
  Purchase #2 $234.86   13.567%   $266.7235   $266.72   $266.70   $266.70  
  Purchase #3 $54.47   7.176%   $58.3788   $58.38   $58.40   $58.40  
  Purchase #4 $115.63   3.549%   $119.7337   $119.73   $119.75   $119.70  
  Purchase #5 $104.78   4.167%   $109.1462   $109.15   $109.15   $109.10  
  Purchase #6 $219.75   11.240%   $244.4499   $244.45   $244.45   $244.40  
  Purchase #7 $204.83   6.199%   $217.5274   $217.53   $217.55   $217.50  
  7 purchase totals = $996.31       $1,081.9503   $1,081.95   $1,082.00   $1,081.80