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 $250.34   6.792%   $267.3431   $267.34   $267.35   $267.30  
  Purchase #2 $181.71   6.396%   $193.3322   $193.33   $193.35   $193.30  
  Purchase #3 $175.65   8.151%   $189.9672   $189.97   $189.95   $190.00  
  Purchase #4 $163.99   5.690%   $173.321   $173.32   $173.30   $173.30  
  Purchase #5 $135.87   6.299%   $144.4285   $144.43   $144.45   $144.40  
  Purchase #6 $164.43   12.428%   $184.8654   $184.87   $184.85   $184.90  
  Purchase #7 $185.46   12.411%   $208.4774   $208.48   $208.50   $208.50  
  7 purchase totals = $1,257.45       $1,361.7348   $1,361.74   $1,361.75   $1,361.70