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 $238.76   3.408%   $246.8969   $246.90   $246.90   $246.90  
  Purchase #2 $192.63   10.815%   $213.4629   $213.46   $213.45   $213.50  
  Purchase #3 $195.87   9.129%   $213.751   $213.75   $213.75   $213.80  
  Purchase #4 $226.71   12.593%   $255.2596   $255.26   $255.25   $255.30  
  Purchase #5 $131.82   3.569%   $136.5247   $136.52   $136.50   $136.50  
  Purchase #6 $25.33   8.813%   $27.5623   $27.56   $27.55   $27.60  
  Purchase #7 $216.82   10.511%   $239.61   $239.61   $239.60   $239.60  
  7 purchase totals = $1,227.94       $1,333.0674   $1,333.06   $1,333.00   $1,333.20