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	$82.26	8.698%	$89.415	$89.42	$89.40	$89.40
Purchase #2	$183.83	12.841%	$207.4356	$207.44	$207.45	$207.40
Purchase #3	$13.82	7.845%	$14.9042	$14.90	$14.90	$14.90
Purchase #4	$129.26	13.773%	$147.063	$147.06	$147.05	$147.10
Purchase #5	$167.76	13.613%	$190.5972	$190.60	$190.60	$190.60
Purchase #6	$33.78	8.731%	$36.7293	$36.73	$36.75	$36.70
Purchase #7	$52.42	4.690%	$54.8785	$54.88	$54.90	$54.90
7 purchase totals =	$663.13		$741.0228	$741.03	$741.05	$741.00