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 $187.49   11.444%   $208.9464   $208.95   $208.95   $208.90  
  Purchase #2 $63.84   8.792%   $69.4528   $69.45   $69.45   $69.50  
  Purchase #3 $28.51   12.866%   $32.1781   $32.18   $32.20   $32.20  
  Purchase #4 $36.92   8.791%   $40.1656   $40.17   $40.15   $40.20  
  Purchase #5 $115.71   9.529%   $126.736   $126.74   $126.75   $126.70  
  Purchase #6 $53.40   4.614%   $55.8639   $55.86   $55.85   $55.90  
  Purchase #7 $86.69   5.658%   $91.5949   $91.59   $91.60   $91.60  
  7 purchase totals = $572.56       $624.9377   $624.94   $624.95   $625.00