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 $197.45   8.859%   $214.9421   $214.94   $214.95   $214.90  
  Purchase #2 $50.99   4.279%   $53.1719   $53.17   $53.15   $53.20  
  Purchase #3 $248.85   13.323%   $282.0043   $282.00   $282.00   $282.00  
  Purchase #4 $237.67   10.182%   $261.8696   $261.87   $261.85   $261.90  
  Purchase #5 $219.29   12.723%   $247.1903   $247.19   $247.20   $247.20  
  Purchase #6 $233.92   6.680%   $249.5459   $249.55   $249.55   $249.50  
  Purchase #7 $166.25   13.550%   $188.7769   $188.78   $188.80   $188.80  
  7 purchase totals = $1,354.42       $1,497.5010   $1,497.50   $1,497.50   $1,497.50