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 $176.74   10.686%   $195.6264   $195.63   $195.65   $195.60  
  Purchase #2 $14.90   3.443%   $15.413   $15.41   $15.40   $15.40  
  Purchase #3 $15.29   8.567%   $16.5999   $16.60   $16.60   $16.60  
  Purchase #4 $145.49   7.430%   $156.2999   $156.30   $156.30   $156.30  
  Purchase #5 $197.29   6.709%   $210.5262   $210.53   $210.55   $210.50  
  Purchase #6 $95.28   6.324%   $101.3055   $101.31   $101.30   $101.30  
  Purchase #7 $49.71   9.809%   $54.5861   $54.59   $54.60   $54.60  
  7 purchase totals = $694.70       $750.3570   $750.37   $750.40   $750.30