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 $66.38   10.301%   $73.2178   $73.22   $73.20   $73.20  
  Purchase #2 $135.91   4.412%   $141.9063   $141.91   $141.90   $141.90  
  Purchase #3 $92.76   4.609%   $97.0353   $97.04   $97.05   $97.00  
  Purchase #4 $83.83   3.119%   $86.4447   $86.44   $86.45   $86.40  
  Purchase #5 $164.78   8.202%   $178.2953   $178.30   $178.30   $178.30  
  Purchase #6 $60.42   4.107%   $62.9014   $62.90   $62.90   $62.90  
  Purchase #7 $108.46   9.438%   $118.6965   $118.70   $118.70   $118.70  
  7 purchase totals = $712.54       $758.4973   $758.51   $758.50   $758.40