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	$54.64	10.391%	$60.3176	$60.32	$60.30	$60.30
Purchase #2	$106.89	3.133%	$110.2389	$110.24	$110.25	$110.20
Purchase #3	$144.89	3.217%	$149.5511	$149.55	$149.55	$149.60
Purchase #4	$127.61	11.592%	$142.4026	$142.40	$142.40	$142.40
Purchase #5	$117.37	11.674%	$131.0718	$131.07	$131.05	$131.10
Purchase #6	$207.61	6.493%	$221.0901	$221.09	$221.10	$221.10
Purchase #7	$52.39	13.608%	$59.5192	$59.52	$59.50	$59.50
7 purchase totals =	$811.40		$874.1913	$874.19	$874.15	$874.20