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 $224.26   11.185%   $249.3435   $249.34   $249.35   $249.30  
  Purchase #2 $16.75   12.804%   $18.8947   $18.89   $18.90   $18.90  
  Purchase #3 $220.85   3.713%   $229.0502   $229.05   $229.05   $229.10  
  Purchase #4 $64.93   13.164%   $73.4774   $73.48   $73.50   $73.50  
  Purchase #5 $109.62   8.819%   $119.2874   $119.29   $119.30   $119.30  
  Purchase #6 $188.48   11.498%   $210.1514   $210.15   $210.15   $210.20  
  Purchase #7 $120.68   10.622%   $133.4986   $133.50   $133.50   $133.50  
  7 purchase totals = $945.57       $1,033.7032   $1,033.70   $1,033.75   $1,033.80