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 $63.68   9.593%   $69.7888   $69.79   $69.80   $69.80  
  Purchase #2 $101.83   6.296%   $108.2412   $108.24   $108.25   $108.20  
  Purchase #3 $183.38   11.181%   $203.8837   $203.88   $203.90   $203.90  
  Purchase #4 $233.63   12.454%   $262.7263   $262.73   $262.75   $262.70  
  Purchase #5 $48.83   5.114%   $51.3272   $51.33   $51.35   $51.30  
  Purchase #6 $157.89   8.528%   $171.3549   $171.35   $171.35   $171.40  
  Purchase #7 $58.66   11.638%   $65.4869   $65.49   $65.50   $65.50  
  7 purchase totals = $847.90       $932.8090   $932.81   $932.90   $932.80