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 $84.71   4.421%   $88.455   $88.46   $88.45   $88.50  
  Purchase #2 $174.56   7.863%   $188.2857   $188.29   $188.30   $188.30  
  Purchase #3 $79.31   9.202%   $86.6081   $86.61   $86.60   $86.60  
  Purchase #4 $217.83   12.246%   $244.5055   $244.51   $244.50   $244.50  
  Purchase #5 $67.79   12.639%   $76.358   $76.36   $76.35   $76.40  
  Purchase #6 $15.30   13.756%   $17.4047   $17.40   $17.40   $17.40  
  Purchase #7 $242.95   9.497%   $266.023   $266.02   $266.00   $266.00  
  7 purchase totals = $882.45       $967.6400   $967.65   $967.60   $967.70