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 $204.28   5.643%   $215.8075   $215.81   $215.80   $215.80  
  Purchase #2 $62.71   8.462%   $68.0165   $68.02   $68.00   $68.00  
  Purchase #3 $74.43   13.128%   $84.2012   $84.20   $84.20   $84.20  
  Purchase #4 $90.96   9.264%   $99.3865   $99.39   $99.40   $99.40  
  Purchase #5 $135.85   13.653%   $154.3976   $154.40   $154.40   $154.40  
  Purchase #6 $103.54   10.706%   $114.625   $114.63   $114.65   $114.60  
  Purchase #7 $22.27   6.802%   $23.7848   $23.78   $23.80   $23.80  
  7 purchase totals = $694.04       $760.2191   $760.23   $760.25   $760.20