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 $236.70   4.456%   $247.2474   $247.25   $247.25   $247.20  
  Purchase #2 $199.37   9.610%   $218.5295   $218.53   $218.55   $218.50  
  Purchase #3 $116.83   13.678%   $132.81   $132.81   $132.80   $132.80  
  Purchase #4 $111.38   12.791%   $125.6266   $125.63   $125.65   $125.60  
  Purchase #5 $247.37   9.797%   $271.6048   $271.60   $271.60   $271.60  
  Purchase #6 $180.46   8.278%   $195.3985   $195.40   $195.40   $195.40  
  Purchase #7 $91.55   12.383%   $102.8866   $102.89   $102.90   $102.90  
  7 purchase totals = $1,183.66       $1,294.1034   $1,294.11   $1,294.15   $1,294.00