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 $13.49   5.784%   $14.2703   $14.27   $14.25   $14.30  
  Purchase #2 $23.25   7.127%   $24.907   $24.91   $24.90   $24.90  
  Purchase #3 $199.36   3.698%   $206.7323   $206.73   $206.75   $206.70  
  Purchase #4 $55.30   4.802%   $57.9555   $57.96   $57.95   $58.00  
  Purchase #5 $86.51   12.812%   $97.5937   $97.59   $97.60   $97.60  
  Purchase #6 $62.57   7.129%   $67.0306   $67.03   $67.05   $67.00  
  Purchase #7 $176.75   3.404%   $182.7666   $182.77   $182.75   $182.80  
  7 purchase totals = $617.23       $651.2560   $651.26   $651.25   $651.30