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 $249.55   10.193%   $274.9866   $274.99   $275.00   $275.00  
  Purchase #2 $30.62   11.704%   $34.2038   $34.20   $34.20   $34.20  
  Purchase #3 $67.72   12.179%   $75.9676   $75.97   $75.95   $76.00  
  Purchase #4 $104.44   8.450%   $113.2652   $113.27   $113.25   $113.30  
  Purchase #5 $68.94   10.247%   $76.0043   $76.00   $76.00   $76.00  
  Purchase #6 $6.56   8.265%   $7.1022   $7.10   $7.10   $7.10  
  Purchase #7 $167.64   4.800%   $175.6867   $175.69   $175.70   $175.70  
  7 purchase totals = $695.47       $757.2164   $757.22   $757.20   $757.30