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 $111.41   7.541%   $119.8114   $119.81   $119.80   $119.80  
  Purchase #2 $73.37   6.584%   $78.2007   $78.20   $78.20   $78.20  
  Purchase #3 $134.97   6.846%   $144.21   $144.21   $144.20   $144.20  
  Purchase #4 $88.75   4.105%   $92.3932   $92.39   $92.40   $92.40  
  Purchase #5 $15.71   7.815%   $16.9377   $16.94   $16.95   $16.90  
  Purchase #6 $173.29   11.687%   $193.5424   $193.54   $193.55   $193.50  
  Purchase #7 $126.90   5.759%   $134.2082   $134.21   $134.20   $134.20  
  7 purchase totals = $724.40       $779.3036   $779.30   $779.30   $779.20