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 $235.57   13.160%   $266.571   $266.57   $266.55   $266.60  
  Purchase #2 $35.89   9.397%   $39.2626   $39.26   $39.25   $39.30  
  Purchase #3 $117.89   12.102%   $132.157   $132.16   $132.15   $132.20  
  Purchase #4 $231.63   10.418%   $255.7612   $255.76   $255.75   $255.80  
  Purchase #5 $207.83   6.732%   $221.8211   $221.82   $221.80   $221.80  
  Purchase #6 $214.35   12.855%   $241.9047   $241.90   $241.90   $241.90  
  Purchase #7 $97.94   8.213%   $105.9838   $105.98   $106.00   $106.00  
  7 purchase totals = $1,141.10       $1,263.4614   $1,263.45   $1,263.40   $1,263.60