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 $235.65   5.802%   $249.3224   $249.32   $249.30   $249.30  
  Purchase #2 $44.76   7.148%   $47.9594   $47.96   $47.95   $48.00  
  Purchase #3 $63.54   12.188%   $71.2843   $71.28   $71.30   $71.30  
  Purchase #4 $199.64   12.682%   $224.9583   $224.96   $224.95   $225.00  
  Purchase #5 $28.85   12.110%   $32.3437   $32.34   $32.35   $32.30  
  Purchase #6 $198.97   5.849%   $210.6078   $210.61   $210.60   $210.60  
  Purchase #7 $196.53   5.282%   $206.9107   $206.91   $206.90   $206.90  
  7 purchase totals = $967.94       $1,043.3866   $1,043.38   $1,043.35   $1,043.40