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 $68.36   11.736%   $76.3827   $76.38   $76.40   $76.40  
  Purchase #2 $44.77   4.525%   $46.7958   $46.80   $46.80   $46.80  
  Purchase #3 $104.49   13.629%   $118.7309   $118.73   $118.75   $118.70  
  Purchase #4 $154.54   10.732%   $171.1252   $171.13   $171.15   $171.10  
  Purchase #5 $47.27   9.855%   $51.9285   $51.93   $51.95   $51.90  
  Purchase #6 $167.85   5.678%   $177.3805   $177.38   $177.40   $177.40  
  Purchase #7 $76.59   7.574%   $82.3909   $82.39   $82.40   $82.40  
  7 purchase totals = $663.87       $724.7345   $724.74   $724.85   $724.70