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 $58.33   5.432%   $61.4985   $61.50   $61.50   $61.50  
  Purchase #2 $249.58   9.374%   $272.9756   $272.98   $273.00   $273.00  
  Purchase #3 $141.37   6.733%   $150.8884   $150.89   $150.90   $150.90  
  Purchase #4 $213.89   9.284%   $233.7475   $233.75   $233.75   $233.70  
  Purchase #5 $119.46   8.770%   $129.9366   $129.94   $129.95   $129.90  
  Purchase #6 $222.25   4.111%   $231.3867   $231.39   $231.40   $231.40  
  Purchase #7 $110.32   13.649%   $125.3776   $125.38   $125.40   $125.40  
  7 purchase totals = $1,115.20       $1,205.8109   $1,205.83   $1,205.90   $1,205.80