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 $230.81   8.196%   $249.7272   $249.73   $249.75   $249.70  
  Purchase #2 $72.79   4.475%   $76.0474   $76.05   $76.05   $76.00  
  Purchase #3 $115.31   7.757%   $124.2546   $124.25   $124.25   $124.30  
  Purchase #4 $11.64   9.458%   $12.7409   $12.74   $12.75   $12.70  
  Purchase #5 $155.51   6.187%   $165.1314   $165.13   $165.15   $165.10  
  Purchase #6 $210.49   5.181%   $221.3955   $221.40   $221.40   $221.40  
  Purchase #7 $105.98   12.409%   $119.1311   $119.13   $119.15   $119.10  
  7 purchase totals = $902.53       $968.4281   $968.43   $968.50   $968.30