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 $211.61   10.130%   $233.0461   $233.05   $233.05   $233.00  
  Purchase #2 $164.78   12.679%   $185.6725   $185.67   $185.65   $185.70  
  Purchase #3 $69.67   13.852%   $79.3207   $79.32   $79.30   $79.30  
  Purchase #4 $239.72   8.271%   $259.5472   $259.55   $259.55   $259.50  
  Purchase #5 $92.32   5.416%   $97.3201   $97.32   $97.30   $97.30  
  Purchase #6 $15.41   7.104%   $16.5047   $16.50   $16.50   $16.50  
  Purchase #7 $23.91   12.624%   $26.9284   $26.93   $26.95   $26.90  
  7 purchase totals = $817.42       $898.3397   $898.34   $898.30   $898.20