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 $145.49   11.758%   $162.5967   $162.60   $162.60   $162.60  
  Purchase #2 $76.43   10.724%   $84.6264   $84.63   $84.65   $84.60  
  Purchase #3 $61.58   12.392%   $69.211   $69.21   $69.20   $69.20  
  Purchase #4 $96.43   8.368%   $104.4993   $104.50   $104.50   $104.50  
  Purchase #5 $72.29   10.136%   $79.6173   $79.62   $79.60   $79.60  
  Purchase #6 $127.59   5.374%   $134.4467   $134.45   $134.45   $134.40  
  Purchase #7 $81.54   10.532%   $90.1278   $90.13   $90.15   $90.10  
  7 purchase totals = $661.35       $725.1252   $725.14   $725.15   $725.00