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 $184.70   8.696%   $200.7615   $200.76   $200.75   $200.80  
  Purchase #2 $171.58   13.690%   $195.0693   $195.07   $195.05   $195.10  
  Purchase #3 $41.40   13.827%   $47.1244   $47.12   $47.10   $47.10  
  Purchase #4 $250.31   8.682%   $272.0419   $272.04   $272.05   $272.00  
  Purchase #5 $119.64   11.546%   $133.4536   $133.45   $133.45   $133.50  
  Purchase #6 $24.91   5.462%   $26.2706   $26.27   $26.25   $26.30  
  Purchase #7 $17.34   3.218%   $17.898   $17.90   $17.90   $17.90  
  7 purchase totals = $809.88       $892.6193   $892.61   $892.55   $892.70