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 $174.55   11.433%   $194.5063   $194.51   $194.50   $194.50  
  Purchase #2 $63.71   3.587%   $65.9953   $66.00   $66.00   $66.00  
  Purchase #3 $233.49   8.573%   $253.5071   $253.51   $253.50   $253.50  
  Purchase #4 $51.92   8.675%   $56.4241   $56.42   $56.40   $56.40  
  Purchase #5 $244.37   5.482%   $257.7664   $257.77   $257.75   $257.80  
  Purchase #6 $111.32   7.582%   $119.7603   $119.76   $119.75   $119.80  
  Purchase #7 $209.80   3.767%   $217.7032   $217.70   $217.70   $217.70  
  7 purchase totals = $1,089.16       $1,165.6627   $1,165.67   $1,165.60   $1,165.70