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 $65.54   13.150%   $74.1585   $74.16   $74.15   $74.20  
  Purchase #2 $94.26   4.294%   $98.3075   $98.31   $98.30   $98.30  
  Purchase #3 $34.30   8.387%   $37.1767   $37.18   $37.20   $37.20  
  Purchase #4 $219.62   4.845%   $230.2606   $230.26   $230.25   $230.30  
  Purchase #5 $125.61   6.642%   $133.953   $133.95   $133.95   $134.00  
  Purchase #6 $188.82   13.606%   $214.5108   $214.51   $214.50   $214.50  
  Purchase #7 $102.31   11.774%   $114.356   $114.36   $114.35   $114.40  
  7 purchase totals = $830.46       $902.7231   $902.73   $902.70   $902.90