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 $247.64   5.643%   $261.6143   $261.61   $261.60   $261.60  
  Purchase #2 $37.88   9.390%   $41.4369   $41.44   $41.45   $41.40  
  Purchase #3 $243.93   7.873%   $263.1346   $263.13   $263.15   $263.10  
  Purchase #4 $116.71   6.730%   $124.5646   $124.56   $124.55   $124.60  
  Purchase #5 $218.54   13.191%   $247.3676   $247.37   $247.35   $247.40  
  Purchase #6 $233.32   13.744%   $265.3875   $265.39   $265.40   $265.40  
  Purchase #7 $238.37   8.748%   $259.2226   $259.22   $259.20   $259.20  
  7 purchase totals = $1,336.39       $1,462.7281   $1,462.72   $1,462.70   $1,462.70