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 $66.88   10.533%   $73.9245   $73.92   $73.90   $73.90  
  Purchase #2 $161.31   7.117%   $172.7904   $172.79   $172.80   $172.80  
  Purchase #3 $118.49   5.727%   $125.2759   $125.28   $125.30   $125.30  
  Purchase #4 $193.88   7.265%   $207.9654   $207.97   $207.95   $208.00  
  Purchase #5 $107.43   10.123%   $118.3051   $118.31   $118.30   $118.30  
  Purchase #6 $47.94   3.434%   $49.5863   $49.59   $49.60   $49.60  
  Purchase #7 $235.38   8.382%   $255.1096   $255.11   $255.10   $255.10  
  7 purchase totals = $931.31       $1,002.9572   $1,002.97   $1,002.95   $1,003.00