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 $241.26   11.633%   $269.3258   $269.33   $269.35   $269.30  
  Purchase #2 $115.61   8.724%   $125.6958   $125.70   $125.70   $125.70  
  Purchase #3 $247.82   4.609%   $259.242   $259.24   $259.25   $259.20  
  Purchase #4 $200.38   10.370%   $221.1594   $221.16   $221.15   $221.20  
  Purchase #5 $65.80   8.486%   $71.3838   $71.38   $71.40   $71.40  
  Purchase #6 $166.74   10.528%   $184.2944   $184.29   $184.30   $184.30  
  Purchase #7 $165.76   12.676%   $186.7717   $186.77   $186.75   $186.80  
  7 purchase totals = $1,203.37       $1,317.8729   $1,317.87   $1,317.90   $1,317.90