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 $87.51   5.639%   $92.4447   $92.44   $92.45   $92.40  
  Purchase #2 $195.95   6.146%   $207.9931   $207.99   $208.00   $208.00  
  Purchase #3 $224.28   7.434%   $240.953   $240.95   $240.95   $241.00  
  Purchase #4 $29.47   11.354%   $32.816   $32.82   $32.80   $32.80  
  Purchase #5 $218.25   11.807%   $244.0188   $244.02   $244.00   $244.00  
  Purchase #6 $112.84   5.590%   $119.1478   $119.15   $119.15   $119.10  
  Purchase #7 $58.28   11.375%   $64.9094   $64.91   $64.90   $64.90  
  7 purchase totals = $926.58       $1,002.2828   $1,002.28   $1,002.25   $1,002.20