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 $112.49   5.806%   $119.0212   $119.02   $119.00   $119.00  
  Purchase #2 $147.63   9.758%   $162.0357   $162.04   $162.05   $162.00  
  Purchase #3 $45.91   3.830%   $47.6684   $47.67   $47.65   $47.70  
  Purchase #4 $198.66   13.831%   $226.1367   $226.14   $226.15   $226.10  
  Purchase #5 $226.29   9.103%   $246.8892   $246.89   $246.90   $246.90  
  Purchase #6 $164.69   12.545%   $185.3504   $185.35   $185.35   $185.40  
  Purchase #7 $160.59   10.398%   $177.2881   $177.29   $177.30   $177.30  
  7 purchase totals = $1,056.26       $1,164.3897   $1,164.40   $1,164.40   $1,164.40