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 $46.51   5.262%   $48.9574   $48.96   $48.95   $49.00  
  Purchase #2 $116.38   12.223%   $130.6051   $130.61   $130.60   $130.60  
  Purchase #3 $97.99   6.349%   $104.2114   $104.21   $104.20   $104.20  
  Purchase #4 $179.62   10.265%   $198.058   $198.06   $198.05   $198.10  
  Purchase #5 $214.77   12.142%   $240.8474   $240.85   $240.85   $240.80  
  Purchase #6 $198.94   5.694%   $210.2676   $210.27   $210.25   $210.30  
  Purchase #7 $24.75   8.706%   $26.9047   $26.90   $26.90   $26.90  
  7 purchase totals = $878.96       $959.8516   $959.86   $959.80   $959.90