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 $240.38   3.170%   $248   $248.00   $248.00   $248.00  
  Purchase #2 $155.68   5.736%   $164.6098   $164.61   $164.60   $164.60  
  Purchase #3 $43.30   12.620%   $48.7645   $48.76   $48.75   $48.80  
  Purchase #4 $47.91   8.271%   $51.8726   $51.87   $51.85   $51.90  
  Purchase #5 $100.61   4.208%   $104.8437   $104.84   $104.85   $104.80  
  Purchase #6 $146.77   11.186%   $163.1877   $163.19   $163.20   $163.20  
  Purchase #7 $219.39   6.269%   $233.1436   $233.14   $233.15   $233.10  
  7 purchase totals = $954.04       $1,014.4219   $1,014.41   $1,014.40   $1,014.40