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	$13.46	11.668%	$15.0305	$15.03	$15.05	$15.00
Purchase #2	$130.50	9.188%	$142.4903	$142.49	$142.50	$142.50
Purchase #3	$155.89	12.176%	$174.8712	$174.87	$174.85	$174.90
Purchase #4	$149.49	13.697%	$169.9656	$169.97	$169.95	$170.00
Purchase #5	$173.89	6.316%	$184.8729	$184.87	$184.85	$184.90
Purchase #6	$164.27	4.565%	$171.7689	$171.77	$171.75	$171.80
Purchase #7	$164.37	13.724%	$186.9281	$186.93	$186.95	$186.90
7 purchase totals =	$951.87		$1,045.9275	$1,045.93	$1,045.90	$1,046.00