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 $22.26   6.598%   $23.7287   $23.73   $23.75   $23.70  
  Purchase #2 $207.87   10.247%   $229.1704   $229.17   $229.15   $229.20  
  Purchase #3 $231.29   8.599%   $251.1786   $251.18   $251.20   $251.20  
  Purchase #4 $50.25   13.393%   $56.98   $56.98   $57.00   $57.00  
  Purchase #5 $136.75   8.611%   $148.5255   $148.53   $148.55   $148.50  
  Purchase #6 $245.43   4.310%   $256.008   $256.01   $256.00   $256.00  
  Purchase #7 $208.77   4.532%   $218.2315   $218.23   $218.25   $218.20  
  7 purchase totals = $1,102.62       $1,183.8227   $1,183.83   $1,183.90   $1,183.80