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 $217.68   13.120%   $246.2396   $246.24   $246.25   $246.20  
  Purchase #2 $125.82   8.309%   $136.2744   $136.27   $136.25   $136.30  
  Purchase #3 $208.37   6.275%   $221.4452   $221.45   $221.45   $221.40  
  Purchase #4 $41.37   4.200%   $43.1075   $43.11   $43.10   $43.10  
  Purchase #5 $104.61   5.612%   $110.4807   $110.48   $110.50   $110.50  
  Purchase #6 $166.76   3.403%   $172.4348   $172.43   $172.45   $172.40  
  Purchase #7 $162.85   13.473%   $184.7908   $184.79   $184.80   $184.80  
  7 purchase totals = $1,027.46       $1,114.7730   $1,114.77   $1,114.80   $1,114.70