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 $48.52   4.328%   $50.6199   $50.62   $50.60   $50.60  
  Purchase #2 $244.25   12.277%   $274.2366   $274.24   $274.25   $274.20  
  Purchase #3 $206.70   12.580%   $232.7029   $232.70   $232.70   $232.70  
  Purchase #4 $21.97   6.610%   $23.4222   $23.42   $23.40   $23.40  
  Purchase #5 $242.60   4.234%   $252.8717   $252.87   $252.85   $252.90  
  Purchase #6 $104.28   9.566%   $114.2554   $114.26   $114.25   $114.30  
  Purchase #7 $14.51   6.477%   $15.4498   $15.45   $15.45   $15.40  
  7 purchase totals = $882.83       $963.5585   $963.56   $963.50   $963.50