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 $247.84   8.598%   $269.1493   $269.15   $269.15   $269.10  
  Purchase #2 $225.41   13.682%   $256.2506   $256.25   $256.25   $256.30  
  Purchase #3 $163.26   9.469%   $178.7191   $178.72   $178.70   $178.70  
  Purchase #4 $127.25   11.144%   $141.4307   $141.43   $141.45   $141.40  
  Purchase #5 $66.88   12.539%   $75.2661   $75.27   $75.25   $75.30  
  Purchase #6 $187.95   9.169%   $205.1831   $205.18   $205.20   $205.20  
  Purchase #7 $66.91   9.491%   $73.2604   $73.26   $73.25   $73.30  
  7 purchase totals = $1,085.50       $1,199.2593   $1,199.26   $1,199.25   $1,199.30