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 $201.65   6.256%   $214.2652   $214.27   $214.25   $214.30  
  Purchase #2 $138.58   13.504%   $157.2938   $157.29   $157.30   $157.30  
  Purchase #3 $96.76   9.423%   $105.8777   $105.88   $105.90   $105.90  
  Purchase #4 $94.72   3.394%   $97.9348   $97.93   $97.95   $97.90  
  Purchase #5 $207.69   9.221%   $226.8411   $226.84   $226.85   $226.80  
  Purchase #6 $246.77   11.460%   $275.0498   $275.05   $275.05   $275.00  
  Purchase #7 $217.69   5.498%   $229.6586   $229.66   $229.65   $229.70  
  7 purchase totals = $1,203.86       $1,306.9210   $1,306.92   $1,306.95   $1,306.90