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 $62.36   5.853%   $66.0099   $66.01   $66.00   $66.00  
  Purchase #2 $89.25   9.452%   $97.6859   $97.69   $97.70   $97.70  
  Purchase #3 $159.56   7.757%   $171.9371   $171.94   $171.95   $171.90  
  Purchase #4 $40.28   9.154%   $43.9672   $43.97   $43.95   $44.00  
  Purchase #5 $163.63   3.219%   $168.8972   $168.90   $168.90   $168.90  
  Purchase #6 $169.83   9.163%   $185.3915   $185.39   $185.40   $185.40  
  Purchase #7 $190.63   6.506%   $203.0324   $203.03   $203.05   $203.00  
  7 purchase totals = $875.54       $936.9212   $936.93   $936.95   $936.90