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 $95.38   3.336%   $98.5619   $98.56   $98.55   $98.60  
  Purchase #2 $229.85   8.502%   $249.3918   $249.39   $249.40   $249.40  
  Purchase #3 $205.94   4.446%   $215.0961   $215.10   $215.10   $215.10  
  Purchase #4 $70.81   11.583%   $79.0119   $79.01   $79.00   $79.00  
  Purchase #5 $69.48   4.386%   $72.5274   $72.53   $72.55   $72.50  
  Purchase #6 $197.42   10.393%   $217.9379   $217.94   $217.95   $217.90  
  Purchase #7 $95.56   6.578%   $101.8459   $101.85   $101.85   $101.80  
  7 purchase totals = $964.44       $1,034.3729   $1,034.38   $1,034.40   $1,034.30