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 $36.87   3.359%   $38.1085   $38.11   $38.10   $38.10  
  Purchase #2 $216.44   13.149%   $244.8997   $244.90   $244.90   $244.90  
  Purchase #3 $168.68   3.564%   $174.6918   $174.69   $174.70   $174.70  
  Purchase #4 $146.59   12.750%   $165.2802   $165.28   $165.30   $165.30  
  Purchase #5 $61.47   12.484%   $69.1439   $69.14   $69.15   $69.10  
  Purchase #6 $68.96   5.505%   $72.7562   $72.76   $72.75   $72.80  
  Purchase #7 $214.36   10.558%   $236.9921   $236.99   $237.00   $237.00  
  7 purchase totals = $913.37       $1,001.8724   $1,001.87   $1,001.90   $1,001.90