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 $54.44   5.112%   $57.223   $57.22   $57.20   $57.20  
  Purchase #2 $192.90   7.291%   $206.9643   $206.96   $206.95   $207.00  
  Purchase #3 $120.82   3.593%   $125.1611   $125.16   $125.15   $125.20  
  Purchase #4 $195.28   11.232%   $217.2138   $217.21   $217.20   $217.20  
  Purchase #5 $185.97   13.160%   $210.4437   $210.44   $210.45   $210.40  
  Purchase #6 $72.71   4.517%   $75.9943   $75.99   $76.00   $76.00  
  Purchase #7 $232.33   11.276%   $258.5275   $258.53   $258.55   $258.50  
  7 purchase totals = $1,054.45       $1,151.5277   $1,151.51   $1,151.50   $1,151.50