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 $61.96   12.732%   $69.8487   $69.85   $69.85   $69.80  
  Purchase #2 $63.58   12.772%   $71.7004   $71.70   $71.70   $71.70  
  Purchase #3 $103.59   13.803%   $117.8885   $117.89   $117.90   $117.90  
  Purchase #4 $17.68   5.326%   $18.6216   $18.62   $18.60   $18.60  
  Purchase #5 $7.84   9.815%   $8.6095   $8.61   $8.60   $8.60  
  Purchase #6 $127.64   3.606%   $132.2427   $132.24   $132.25   $132.20  
  Purchase #7 $72.41   5.765%   $76.5844   $76.58   $76.60   $76.60  
  7 purchase totals = $454.70       $495.4958   $495.49   $495.50   $495.40