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 $216.76   11.277%   $241.204   $241.20   $241.20   $241.20  
  Purchase #2 $102.64   8.566%   $111.4321   $111.43   $111.45   $111.40  
  Purchase #3 $20.56   13.554%   $23.3467   $23.35   $23.35   $23.30  
  Purchase #4 $20.63   3.677%   $21.3886   $21.39   $21.40   $21.40  
  Purchase #5 $77.49   5.775%   $81.965   $81.97   $81.95   $82.00  
  Purchase #6 $166.56   11.196%   $185.2081   $185.21   $185.20   $185.20  
  Purchase #7 $30.52   13.851%   $34.7473   $34.75   $34.75   $34.70  
  7 purchase totals = $635.16       $699.2918   $699.30   $699.30   $699.20