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 $66.50   13.715%   $75.6205   $75.62   $75.60   $75.60  
  Purchase #2 $167.28   6.802%   $178.6584   $178.66   $178.65   $178.70  
  Purchase #3 $203.74   3.223%   $210.3065   $210.31   $210.30   $210.30  
  Purchase #4 $100.86   10.413%   $111.3626   $111.36   $111.35   $111.40  
  Purchase #5 $194.27   11.805%   $217.2036   $217.20   $217.20   $217.20  
  Purchase #6 $69.28   10.198%   $76.3452   $76.35   $76.35   $76.30  
  Purchase #7 $134.65   13.603%   $152.9664   $152.97   $152.95   $153.00  
  7 purchase totals = $936.58       $1,022.4632   $1,022.47   $1,022.40   $1,022.50