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 $41.68   12.147%   $46.7429   $46.74   $46.75   $46.70  
  Purchase #2 $23.46   13.306%   $26.5816   $26.58   $26.60   $26.60  
  Purchase #3 $209.89   10.134%   $231.1603   $231.16   $231.15   $231.20  
  Purchase #4 $154.38   8.403%   $167.3526   $167.35   $167.35   $167.40  
  Purchase #5 $204.63   4.361%   $213.5539   $213.55   $213.55   $213.60  
  Purchase #6 $78.64   6.826%   $84.008   $84.01   $84.00   $84.00  
  Purchase #7 $183.78   6.640%   $195.983   $195.98   $196.00   $196.00  
  7 purchase totals = $896.46       $965.3823   $965.37   $965.40   $965.50