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 $226.99   5.407%   $239.2633   $239.26   $239.25   $239.30  
  Purchase #2 $112.42   8.723%   $122.2264   $122.23   $122.25   $122.20  
  Purchase #3 $63.54   12.478%   $71.4685   $71.47   $71.45   $71.50  
  Purchase #4 $37.64   6.830%   $40.2108   $40.21   $40.20   $40.20  
  Purchase #5 $207.66   6.620%   $221.4071   $221.41   $221.40   $221.40  
  Purchase #6 $248.50   5.553%   $262.2992   $262.30   $262.30   $262.30  
  Purchase #7 $85.64   9.532%   $93.8032   $93.80   $93.80   $93.80  
  7 purchase totals = $982.39       $1,050.6785   $1,050.68   $1,050.65   $1,050.70