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 $96.45   13.221%   $109.2017   $109.20   $109.20   $109.20  
  Purchase #2 $22.41   11.544%   $24.997   $25.00   $25.00   $25.00  
  Purchase #3 $231.40   7.841%   $249.5441   $249.54   $249.55   $249.50  
  Purchase #4 $52.68   13.872%   $59.9878   $59.99   $60.00   $60.00  
  Purchase #5 $62.89   11.392%   $70.0544   $70.05   $70.05   $70.10  
  Purchase #6 $119.97   4.766%   $125.6878   $125.69   $125.70   $125.70  
  Purchase #7 $242.99   5.345%   $255.9778   $255.98   $256.00   $256.00  
  7 purchase totals = $828.79       $895.4506   $895.45   $895.50   $895.50