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 $231.39   13.508%   $262.6462   $262.65   $262.65   $262.60  
  Purchase #2 $26.97   5.636%   $28.49   $28.49   $28.50   $28.50  
  Purchase #3 $236.63   11.556%   $263.975   $263.98   $264.00   $264.00  
  Purchase #4 $250.84   9.624%   $274.9808   $274.98   $275.00   $275.00  
  Purchase #5 $211.53   11.536%   $235.9321   $235.93   $235.95   $235.90  
  Purchase #6 $187.41   13.720%   $213.1227   $213.12   $213.10   $213.10  
  Purchase #7 $213.25   8.165%   $230.6619   $230.66   $230.65   $230.70  
  7 purchase totals = $1,358.02       $1,509.8087   $1,509.81   $1,509.85   $1,509.80