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 $182.42   13.271%   $206.629   $206.63   $206.65   $206.60  
  Purchase #2 $101.32   12.489%   $113.9739   $113.97   $113.95   $114.00  
  Purchase #3 $174.82   9.275%   $191.0346   $191.03   $191.05   $191.00  
  Purchase #4 $244.54   10.628%   $270.5297   $270.53   $270.55   $270.50  
  Purchase #5 $116.64   7.573%   $125.4731   $125.47   $125.45   $125.50  
  Purchase #6 $227.49   6.440%   $242.1404   $242.14   $242.15   $242.10  
  Purchase #7 $61.60   6.790%   $65.7826   $65.78   $65.80   $65.80  
  7 purchase totals = $1,108.83       $1,215.5633   $1,215.55   $1,215.60   $1,215.50