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 $194.29   6.355%   $206.6371   $206.64   $206.65   $206.60  
  Purchase #2 $164.74   6.138%   $174.8517   $174.85   $174.85   $174.90  
  Purchase #3 $51.65   5.312%   $54.3936   $54.39   $54.40   $54.40  
  Purchase #4 $67.33   13.682%   $76.5421   $76.54   $76.55   $76.50  
  Purchase #5 $65.55   3.322%   $67.7276   $67.73   $67.75   $67.70  
  Purchase #6 $182.38   8.125%   $197.1984   $197.20   $197.20   $197.20  
  Purchase #7 $201.72   13.652%   $229.2588   $229.26   $229.25   $229.30  
  7 purchase totals = $927.66       $1,006.6093   $1,006.61   $1,006.65   $1,006.60