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 $48.26   4.754%   $50.5543   $50.55   $50.55   $50.60  
  Purchase #2 $214.86   5.361%   $226.3786   $226.38   $226.40   $226.40  
  Purchase #3 $225.39   6.259%   $239.4972   $239.50   $239.50   $239.50  
  Purchase #4 $156.94   4.612%   $164.1781   $164.18   $164.20   $164.20  
  Purchase #5 $12.84   10.861%   $14.2346   $14.23   $14.25   $14.20  
  Purchase #6 $70.60   11.183%   $78.4952   $78.50   $78.50   $78.50  
  Purchase #7 $133.48   5.331%   $140.5958   $140.60   $140.60   $140.60  
  7 purchase totals = $862.37       $913.9338   $913.94   $914.00   $914.00