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 $88.76   9.216%   $96.9401   $96.94   $96.95   $96.90  
  Purchase #2 $168.51   5.105%   $177.1124   $177.11   $177.10   $177.10  
  Purchase #3 $131.27   4.788%   $137.5552   $137.56   $137.55   $137.60  
  Purchase #4 $69.38   9.296%   $75.8296   $75.83   $75.85   $75.80  
  Purchase #5 $227.39   12.183%   $255.0929   $255.09   $255.10   $255.10  
  Purchase #6 $213.92   4.694%   $223.9614   $223.96   $223.95   $224.00  
  Purchase #7 $245.54   5.826%   $259.8452   $259.85   $259.85   $259.80  
  7 purchase totals = $1,144.77       $1,226.3368   $1,226.34   $1,226.35   $1,226.30