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 $246.65   7.721%   $265.6938   $265.69   $265.70   $265.70  
  Purchase #2 $48.76   13.729%   $55.4543   $55.45   $55.45   $55.50  
  Purchase #3 $157.76   11.653%   $176.1438   $176.14   $176.15   $176.10  
  Purchase #4 $226.31   3.386%   $233.9729   $233.97   $233.95   $234.00  
  Purchase #5 $175.62   8.773%   $191.0271   $191.03   $191.05   $191.00  
  Purchase #6 $188.49   10.336%   $207.9723   $207.97   $207.95   $208.00  
  Purchase #7 $205.57   11.460%   $229.1283   $229.13   $229.15   $229.10  
  7 purchase totals = $1,249.16       $1,359.3925   $1,359.38   $1,359.40   $1,359.40