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 $244.67   3.607%   $253.4952   $253.50   $253.50   $253.50  
  Purchase #2 $58.53   13.128%   $66.2138   $66.21   $66.20   $66.20  
  Purchase #3 $128.34   6.281%   $136.401   $136.40   $136.40   $136.40  
  Purchase #4 $16.71   4.183%   $17.409   $17.41   $17.40   $17.40  
  Purchase #5 $28.38   5.363%   $29.902   $29.90   $29.90   $29.90  
  Purchase #6 $237.66   5.782%   $251.4015   $251.40   $251.40   $251.40  
  Purchase #7 $193.32   10.816%   $214.2295   $214.23   $214.25   $214.20  
  7 purchase totals = $907.61       $969.0520   $969.05   $969.05   $969.00