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 $108.74   10.114%   $119.738   $119.74   $119.75   $119.70  
  Purchase #2 $24.95   8.227%   $27.0026   $27.00   $27.00   $27.00  
  Purchase #3 $30.25   7.806%   $32.6113   $32.61   $32.60   $32.60  
  Purchase #4 $167.55   12.175%   $187.9492   $187.95   $187.95   $187.90  
  Purchase #5 $14.89   10.246%   $16.4156   $16.42   $16.40   $16.40  
  Purchase #6 $56.44   6.236%   $59.9596   $59.96   $59.95   $60.00  
  Purchase #7 $133.25   7.242%   $142.9   $142.90   $142.90   $142.90  
  7 purchase totals = $536.07       $586.5763   $586.58   $586.55   $586.50