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 $56.94   6.306%   $60.5306   $60.53   $60.55   $60.50  
  Purchase #2 $221.68   3.426%   $229.2748   $229.27   $229.25   $229.30  
  Purchase #3 $11.46   8.664%   $12.4529   $12.45   $12.45   $12.50  
  Purchase #4 $105.71   9.376%   $115.6214   $115.62   $115.60   $115.60  
  Purchase #5 $166.34   5.696%   $175.8147   $175.81   $175.80   $175.80  
  Purchase #6 $116.82   6.781%   $124.7416   $124.74   $124.75   $124.70  
  Purchase #7 $62.41   11.712%   $69.7195   $69.72   $69.70   $69.70  
  7 purchase totals = $741.36       $788.1555   $788.14   $788.10   $788.10