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 $115.90   5.676%   $122.4785   $122.48   $122.50   $122.50  
  Purchase #2 $26.77   3.175%   $27.6199   $27.62   $27.60   $27.60  
  Purchase #3 $135.96   7.649%   $146.3596   $146.36   $146.35   $146.40  
  Purchase #4 $145.30   10.711%   $160.8631   $160.86   $160.85   $160.90  
  Purchase #5 $56.74   4.728%   $59.4227   $59.42   $59.40   $59.40  
  Purchase #6 $17.34   9.284%   $18.9498   $18.95   $18.95   $18.90  
  Purchase #7 $9.87   4.574%   $10.3215   $10.32   $10.30   $10.30  
  7 purchase totals = $507.88       $546.0151   $546.01   $545.95   $546.00