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 $205.76   5.451%   $216.976   $216.98   $217.00   $217.00  
  Purchase #2 $8.69   6.748%   $9.2764   $9.28   $9.30   $9.30  
  Purchase #3 $225.87   8.636%   $245.3761   $245.38   $245.40   $245.40  
  Purchase #4 $53.25   11.546%   $59.3982   $59.40   $59.40   $59.40  
  Purchase #5 $107.64   10.552%   $118.9982   $119.00   $119.00   $119.00  
  Purchase #6 $233.87   8.257%   $253.1806   $253.18   $253.20   $253.20  
  Purchase #7 $64.83   12.746%   $73.0932   $73.09   $73.10   $73.10  
  7 purchase totals = $899.91       $976.2987   $976.31   $976.40   $976.40