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 $226.42   9.642%   $248.2514   $248.25   $248.25   $248.30  
  Purchase #2 $125.49   4.632%   $131.3027   $131.30   $131.30   $131.30  
  Purchase #3 $150.78   12.627%   $169.819   $169.82   $169.80   $169.80  
  Purchase #4 $232.72   9.869%   $255.6871   $255.69   $255.70   $255.70  
  Purchase #5 $69.62   10.561%   $76.9726   $76.97   $76.95   $77.00  
  Purchase #6 $190.32   12.211%   $213.56   $213.56   $213.55   $213.60  
  Purchase #7 $244.63   10.531%   $270.392   $270.39   $270.40   $270.40  
  7 purchase totals = $1,239.98       $1,365.9848   $1,365.98   $1,365.95   $1,366.10