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 $57.82   12.367%   $64.9706   $64.97   $64.95   $65.00  
  Purchase #2 $195.78   11.823%   $218.9271   $218.93   $218.95   $218.90  
  Purchase #3 $79.48   11.598%   $88.6981   $88.70   $88.70   $88.70  
  Purchase #4 $184.47   8.492%   $200.1352   $200.14   $200.15   $200.10  
  Purchase #5 $46.46   7.344%   $49.872   $49.87   $49.85   $49.90  
  Purchase #6 $96.77   4.622%   $101.2427   $101.24   $101.25   $101.20  
  Purchase #7 $68.65   13.221%   $77.7262   $77.73   $77.75   $77.70  
  7 purchase totals = $729.43       $801.5719   $801.58   $801.60   $801.50