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 $175.98   8.164%   $190.347   $190.35   $190.35   $190.30  
  Purchase #2 $236.79   8.853%   $257.753   $257.75   $257.75   $257.80  
  Purchase #3 $108.63   6.841%   $116.0614   $116.06   $116.05   $116.10  
  Purchase #4 $236.57   5.593%   $249.8014   $249.80   $249.80   $249.80  
  Purchase #5 $230.91   13.156%   $261.2885   $261.29   $261.30   $261.30  
  Purchase #6 $249.72   7.521%   $268.5014   $268.50   $268.50   $268.50  
  Purchase #7 $90.68   11.867%   $101.441   $101.44   $101.45   $101.40  
  7 purchase totals = $1,329.28       $1,445.1937   $1,445.19   $1,445.20   $1,445.20