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 $239.39   4.111%   $249.2313   $249.23   $249.25   $249.20  
  Purchase #2 $76.45   6.149%   $81.1509   $81.15   $81.15   $81.20  
  Purchase #3 $89.40   9.108%   $97.5426   $97.54   $97.55   $97.50  
  Purchase #4 $184.73   5.149%   $194.2417   $194.24   $194.25   $194.20  
  Purchase #5 $159.74   4.476%   $166.89   $166.89   $166.90   $166.90  
  Purchase #6 $197.89   4.765%   $207.3195   $207.32   $207.30   $207.30  
  Purchase #7 $191.44   8.207%   $207.1515   $207.15   $207.15   $207.20  
  7 purchase totals = $1,139.04       $1,203.5275   $1,203.52   $1,203.55   $1,203.50