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 $215.96   11.647%   $241.1129   $241.11   $241.10   $241.10  
  Purchase #2 $31.70   12.859%   $35.7763   $35.78   $35.80   $35.80  
  Purchase #3 $213.65   12.176%   $239.664   $239.66   $239.65   $239.70  
  Purchase #4 $45.62   9.713%   $50.0511   $50.05   $50.05   $50.10  
  Purchase #5 $25.86   10.775%   $28.6464   $28.65   $28.65   $28.60  
  Purchase #6 $187.99   6.105%   $199.4668   $199.47   $199.45   $199.50  
  Purchase #7 $230.87   3.540%   $239.0428   $239.04   $239.05   $239.00  
  7 purchase totals = $951.65       $1,033.7603   $1,033.76   $1,033.75   $1,033.80