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 $217.54   13.832%   $247.6301   $247.63   $247.65   $247.60  
  Purchase #2 $43.55   8.509%   $47.2557   $47.26   $47.25   $47.30  
  Purchase #3 $141.77   5.227%   $149.1803   $149.18   $149.20   $149.20  
  Purchase #4 $60.41   10.148%   $66.5404   $66.54   $66.55   $66.50  
  Purchase #5 $99.33   11.604%   $110.8563   $110.86   $110.85   $110.90  
  Purchase #6 $27.73   3.712%   $28.7593   $28.76   $28.75   $28.80  
  Purchase #7 $89.63   13.501%   $101.7309   $101.73   $101.75   $101.70  
  7 purchase totals = $679.96       $751.9530   $751.96   $752.00   $752.00