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 $243.64   9.730%   $267.3462   $267.35   $267.35   $267.30  
  Purchase #2 $201.47   11.191%   $224.0165   $224.02   $224.00   $224.00  
  Purchase #3 $30.64   13.868%   $34.8892   $34.89   $34.90   $34.90  
  Purchase #4 $52.77   3.522%   $54.6286   $54.63   $54.65   $54.60  
  Purchase #5 $66.41   9.662%   $72.8265   $72.83   $72.85   $72.80  
  Purchase #6 $81.68   13.698%   $92.8685   $92.87   $92.85   $92.90  
  Purchase #7 $54.70   3.839%   $56.7999   $56.80   $56.80   $56.80  
  7 purchase totals = $731.31       $803.3754   $803.39   $803.40   $803.30