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 $208.94   4.129%   $217.5671   $217.57   $217.55   $217.60  
  Purchase #2 $126.86   13.434%   $143.9024   $143.90   $143.90   $143.90  
  Purchase #3 $162.48   8.613%   $176.4744   $176.47   $176.45   $176.50  
  Purchase #4 $233.35   11.274%   $259.6579   $259.66   $259.65   $259.70  
  Purchase #5 $106.30   5.752%   $112.4144   $112.41   $112.40   $112.40  
  Purchase #6 $217.40   6.232%   $230.9484   $230.95   $230.95   $230.90  
  Purchase #7 $47.28   13.836%   $53.8217   $53.82   $53.80   $53.80  
  7 purchase totals = $1,102.61       $1,194.7863   $1,194.78   $1,194.70   $1,194.80