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 $61.27   9.627%   $67.1685   $67.17   $67.15   $67.20  
  Purchase #2 $144.73   8.774%   $157.4286   $157.43   $157.45   $157.40  
  Purchase #3 $64.97   9.537%   $71.1662   $71.17   $71.15   $71.20  
  Purchase #4 $115.72   5.858%   $122.4989   $122.50   $122.50   $122.50  
  Purchase #5 $170.64   8.531%   $185.1973   $185.20   $185.20   $185.20  
  Purchase #6 $33.63   6.645%   $35.8647   $35.86   $35.85   $35.90  
  Purchase #7 $117.89   11.748%   $131.7397   $131.74   $131.75   $131.70  
  7 purchase totals = $708.85       $771.0639   $771.07   $771.05   $771.10