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 $23.95   8.158%   $25.9038   $25.90   $25.90   $25.90  
  Purchase #2 $56.89   10.105%   $62.6387   $62.64   $62.65   $62.60  
  Purchase #3 $31.86   6.823%   $34.0338   $34.03   $34.05   $34.00  
  Purchase #4 $113.74   10.485%   $125.6656   $125.67   $125.65   $125.70  
  Purchase #5 $29.66   5.293%   $31.2299   $31.23   $31.25   $31.20  
  Purchase #6 $173.66   12.459%   $195.2963   $195.30   $195.30   $195.30  
  Purchase #7 $229.53   11.304%   $255.4761   $255.48   $255.50   $255.50  
  7 purchase totals = $659.29       $730.2442   $730.25   $730.30   $730.20