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 $64.48   10.189%   $71.0499   $71.05   $71.05   $71.00  
  Purchase #2 $115.81   8.313%   $125.4373   $125.44   $125.45   $125.40  
  Purchase #3 $19.34   9.564%   $21.1897   $21.19   $21.20   $21.20  
  Purchase #4 $195.70   9.498%   $214.2876   $214.29   $214.30   $214.30  
  Purchase #5 $96.51   3.795%   $100.1726   $100.17   $100.15   $100.20  
  Purchase #6 $149.41   12.441%   $167.9981   $168.00   $168.00   $168.00  
  Purchase #7 $226.39   11.333%   $252.0468   $252.05   $252.05   $252.00  
  7 purchase totals = $867.64       $952.1820   $952.19   $952.20   $952.10