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 $96.27   8.530%   $104.4818   $104.48   $104.50   $104.50  
  Purchase #2 $62.61   4.296%   $65.2997   $65.30   $65.30   $65.30  
  Purchase #3 $53.33   11.657%   $59.5467   $59.55   $59.55   $59.50  
  Purchase #4 $240.75   4.125%   $250.6809   $250.68   $250.70   $250.70  
  Purchase #5 $73.80   13.817%   $83.9969   $84.00   $84.00   $84.00  
  Purchase #6 $35.66   13.756%   $40.5654   $40.57   $40.55   $40.60  
  Purchase #7 $242.99   10.165%   $267.6899   $267.69   $267.70   $267.70  
  7 purchase totals = $805.41       $872.2613   $872.27   $872.30   $872.30