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 $245.36   11.170%   $272.7667   $272.77   $272.75   $272.80  
  Purchase #2 $160.47   10.643%   $177.5488   $177.55   $177.55   $177.50  
  Purchase #3 $185.86   6.215%   $197.4112   $197.41   $197.40   $197.40  
  Purchase #4 $248.92   10.613%   $275.3379   $275.34   $275.35   $275.30  
  Purchase #5 $126.36   5.645%   $133.493   $133.49   $133.50   $133.50  
  Purchase #6 $196.42   6.490%   $209.1677   $209.17   $209.15   $209.20  
  Purchase #7 $245.26   6.683%   $261.6507   $261.65   $261.65   $261.70  
  7 purchase totals = $1,408.65       $1,527.3760   $1,527.38   $1,527.35   $1,527.40