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 $47.96   12.856%   $54.1257   $54.13   $54.15   $54.10  
  Purchase #2 $236.43   11.215%   $262.9456   $262.95   $262.95   $262.90  
  Purchase #3 $10.67   5.828%   $11.2918   $11.29   $11.30   $11.30  
  Purchase #4 $68.40   8.597%   $74.2803   $74.28   $74.30   $74.30  
  Purchase #5 $5.62   3.123%   $5.7955   $5.80   $5.80   $5.80  
  Purchase #6 $107.99   6.403%   $114.9046   $114.90   $114.90   $114.90  
  Purchase #7 $177.26   12.596%   $199.5877   $199.59   $199.60   $199.60  
  7 purchase totals = $654.33       $722.9312   $722.94   $723.00   $722.90