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	$66.92	6.168%	$71.0476	$71.05	$71.05	$71.00
Purchase #2	$55.91	4.186%	$58.2504	$58.25	$58.25	$58.30
Purchase #3	$51.71	13.228%	$58.5502	$58.55	$58.55	$58.60
Purchase #4	$12.28	5.530%	$12.9591	$12.96	$12.95	$13.00
Purchase #5	$147.41	12.496%	$165.8304	$165.83	$165.85	$165.80
Purchase #6	$60.65	11.605%	$67.6884	$67.69	$67.70	$67.70
Purchase #7	$55.60	6.864%	$59.4164	$59.42	$59.40	$59.40
7 purchase totals =	$450.48		$493.7425	$493.75	$493.75	$493.80