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 $239.72   11.441%   $267.1464   $267.15   $267.15   $267.10  
  Purchase #2 $70.82   7.306%   $75.9941   $75.99   $76.00   $76.00  
  Purchase #3 $151.30   5.355%   $159.4021   $159.40   $159.40   $159.40  
  Purchase #4 $68.30   11.128%   $75.9004   $75.90   $75.90   $75.90  
  Purchase #5 $250.26   10.689%   $277.0103   $277.01   $277.00   $277.00  
  Purchase #6 $213.31   9.502%   $233.5787   $233.58   $233.60   $233.60  
  Purchase #7 $100.92   3.758%   $104.7126   $104.71   $104.70   $104.70  
  7 purchase totals = $1,094.63       $1,193.7446   $1,193.74   $1,193.75   $1,193.70