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 $148.54   6.544%   $158.2605   $158.26   $158.25   $158.30  
  Purchase #2 $155.93   13.474%   $176.94   $176.94   $176.95   $176.90  
  Purchase #3 $5.76   12.183%   $6.4617   $6.46   $6.45   $6.50  
  Purchase #4 $97.96   12.246%   $109.9562   $109.96   $109.95   $110.00  
  Purchase #5 $217.99   4.458%   $227.708   $227.71   $227.70   $227.70  
  Purchase #6 $150.62   12.533%   $169.4972   $169.50   $169.50   $169.50  
  Purchase #7 $109.68   6.684%   $117.011   $117.01   $117.00   $117.00  
  7 purchase totals = $886.48       $965.8346   $965.84   $965.80   $965.90