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 $249.55   4.448%   $260.65   $260.65   $260.65   $260.70  
  Purchase #2 $102.71   13.523%   $116.5995   $116.60   $116.60   $116.60  
  Purchase #3 $68.63   12.424%   $77.1566   $77.16   $77.15   $77.20  
  Purchase #4 $248.61   7.375%   $266.945   $266.95   $266.95   $266.90  
  Purchase #5 $239.37   12.365%   $268.9681   $268.97   $268.95   $269.00  
  Purchase #6 $120.77   11.548%   $134.7165   $134.72   $134.70   $134.70  
  Purchase #7 $212.63   9.294%   $232.3918   $232.39   $232.40   $232.40  
  7 purchase totals = $1,242.27       $1,357.4275   $1,357.44   $1,357.40   $1,357.50