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 $204.51   6.104%   $216.9933   $216.99   $217.00   $217.00  
  Purchase #2 $86.64   8.257%   $93.7939   $93.79   $93.80   $93.80  
  Purchase #3 $158.63   11.402%   $176.717   $176.72   $176.70   $176.70  
  Purchase #4 $58.61   9.622%   $64.2495   $64.25   $64.25   $64.20  
  Purchase #5 $86.74   11.469%   $96.6882   $96.69   $96.70   $96.70  
  Purchase #6 $64.26   10.513%   $71.0157   $71.02   $71.00   $71.00  
  Purchase #7 $217.35   11.614%   $242.593   $242.59   $242.60   $242.60  
  7 purchase totals = $876.74       $962.0506   $962.05   $962.05   $962.00