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	$179.30	13.790%	$204.0255	$204.03	$204.05	$204.00
Purchase #2	$150.30	10.792%	$166.5204	$166.52	$166.50	$166.50
Purchase #3	$112.92	12.716%	$127.2789	$127.28	$127.30	$127.30
Purchase #4	$202.94	11.551%	$226.3816	$226.38	$226.40	$226.40
Purchase #5	$63.55	5.200%	$66.8546	$66.85	$66.85	$66.90
Purchase #6	$74.26	5.424%	$78.2879	$78.29	$78.30	$78.30
Purchase #7	$116.48	6.482%	$124.0302	$124.03	$124.05	$124.00
7 purchase totals =	$899.75		$993.3791	$993.38	$993.45	$993.40