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 $60.80   11.626%   $67.8686   $67.87   $67.85   $67.90  
  Purchase #2 $14.29   4.260%   $14.8988   $14.90   $14.90   $14.90  
  Purchase #3 $247.81   12.645%   $279.1456   $279.15   $279.15   $279.10  
  Purchase #4 $44.77   13.504%   $50.8157   $50.82   $50.80   $50.80  
  Purchase #5 $115.41   7.481%   $124.0438   $124.04   $124.05   $124.00  
  Purchase #6 $151.60   7.136%   $162.4182   $162.42   $162.40   $162.40  
  Purchase #7 $94.66   3.116%   $97.6096   $97.61   $97.60   $97.60  
  7 purchase totals = $729.34       $796.8003   $796.81   $796.75   $796.70