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 $82.88   11.571%   $92.47   $92.47   $92.45   $92.50  
  Purchase #2 $208.94   12.304%   $234.648   $234.65   $234.65   $234.60  
  Purchase #3 $156.48   4.126%   $162.9364   $162.94   $162.95   $162.90  
  Purchase #4 $170.85   7.154%   $183.0726   $183.07   $183.05   $183.10  
  Purchase #5 $227.57   12.475%   $255.9594   $255.96   $255.95   $256.00  
  Purchase #6 $21.37   11.191%   $23.7615   $23.76   $23.75   $23.80  
  Purchase #7 $37.85   4.185%   $39.434   $39.43   $39.45   $39.40  
  7 purchase totals = $905.94       $992.2819   $992.28   $992.25   $992.30