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 $180.74   9.347%   $197.6338   $197.63   $197.65   $197.60  
  Purchase #2 $240.48   10.574%   $265.9084   $265.91   $265.90   $265.90  
  Purchase #3 $158.79   4.147%   $165.375   $165.38   $165.40   $165.40  
  Purchase #4 $248.95   5.378%   $262.3385   $262.34   $262.35   $262.30  
  Purchase #5 $214.88   12.278%   $241.263   $241.26   $241.25   $241.30  
  Purchase #6 $54.92   10.665%   $60.7772   $60.78   $60.80   $60.80  
  Purchase #7 $191.68   10.312%   $211.446   $211.45   $211.45   $211.40  
  7 purchase totals = $1,290.44       $1,404.7419   $1,404.75   $1,404.80   $1,404.70