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 $34.51   4.846%   $36.1824   $36.18   $36.20   $36.20  
  Purchase #2 $108.95   4.217%   $113.5444   $113.54   $113.55   $113.50  
  Purchase #3 $13.48   8.744%   $14.6587   $14.66   $14.65   $14.70  
  Purchase #4 $206.37   5.373%   $217.4583   $217.46   $217.45   $217.50  
  Purchase #5 $125.74   9.536%   $137.7306   $137.73   $137.75   $137.70  
  Purchase #6 $208.42   3.207%   $215.104   $215.10   $215.10   $215.10  
  Purchase #7 $94.81   6.494%   $100.967   $100.97   $100.95   $101.00  
  7 purchase totals = $792.28       $835.6454   $835.64   $835.65   $835.70