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 $169.53   4.214%   $176.674   $176.67   $176.65   $176.70  
  Purchase #2 $69.98   5.218%   $73.6316   $73.63   $73.65   $73.60  
  Purchase #3 $28.38   7.569%   $30.5281   $30.53   $30.55   $30.50  
  Purchase #4 $205.52   13.110%   $232.4637   $232.46   $232.45   $232.50  
  Purchase #5 $67.99   6.460%   $72.3822   $72.38   $72.40   $72.40  
  Purchase #6 $59.30   6.772%   $63.3158   $63.32   $63.30   $63.30  
  Purchase #7 $155.72   13.617%   $176.9244   $176.92   $176.90   $176.90  
  7 purchase totals = $756.42       $825.9198   $825.91   $825.90   $825.90