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 $232.77   3.657%   $241.2824   $241.28   $241.30   $241.30  
  Purchase #2 $183.78   6.289%   $195.3379   $195.34   $195.35   $195.30  
  Purchase #3 $163.57   12.414%   $183.8756   $183.88   $183.90   $183.90  
  Purchase #4 $216.83   8.454%   $235.1608   $235.16   $235.15   $235.20  
  Purchase #5 $178.25   10.680%   $197.2871   $197.29   $197.30   $197.30  
  Purchase #6 $123.75   10.553%   $136.8093   $136.81   $136.80   $136.80  
  Purchase #7 $128.99   8.150%   $139.5027   $139.50   $139.50   $139.50  
  7 purchase totals = $1,227.94       $1,329.2558   $1,329.26   $1,329.30   $1,329.30