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 $60.36   12.217%   $67.7342   $67.73   $67.75   $67.70  
  Purchase #2 $6.71   7.137%   $7.1889   $7.19   $7.20   $7.20  
  Purchase #3 $161.33   7.486%   $173.4072   $173.41   $173.40   $173.40  
  Purchase #4 $88.56   8.401%   $95.9999   $96.00   $96.00   $96.00  
  Purchase #5 $42.89   8.839%   $46.681   $46.68   $46.70   $46.70  
  Purchase #6 $90.37   5.311%   $95.1696   $95.17   $95.15   $95.20  
  Purchase #7 $29.95   9.376%   $32.7581   $32.76   $32.75   $32.80  
  7 purchase totals = $480.17       $518.9389   $518.94   $518.95   $519.00