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 $58.36   12.460%   $65.6317   $65.63   $65.65   $65.60  
  Purchase #2 $187.63   4.205%   $195.5198   $195.52   $195.50   $195.50  
  Purchase #3 $166.62   4.841%   $174.6861   $174.69   $174.70   $174.70  
  Purchase #4 $50.42   8.182%   $54.5454   $54.55   $54.55   $54.50  
  Purchase #5 $162.84   12.166%   $182.6511   $182.65   $182.65   $182.70  
  Purchase #6 $94.77   3.324%   $97.9202   $97.92   $97.90   $97.90  
  Purchase #7 $61.83   5.660%   $65.3296   $65.33   $65.35   $65.30  
  7 purchase totals = $782.47       $836.2839   $836.29   $836.30   $836.20