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	$92.33	8.124%	$99.8309	$99.83	$99.85	$99.80
Purchase #2	$235.44	10.297%	$259.6833	$259.68	$259.70	$259.70
Purchase #3	$219.42	4.871%	$230.1079	$230.11	$230.10	$230.10
Purchase #4	$103.46	8.152%	$111.8941	$111.89	$111.90	$111.90
Purchase #5	$239.33	12.586%	$269.4521	$269.45	$269.45	$269.50
Purchase #6	$23.40	11.618%	$26.1186	$26.12	$26.10	$26.10
Purchase #7	$167.78	3.252%	$173.2362	$173.24	$173.25	$173.20
7 purchase totals =	$1,081.16		$1,170.3231	$1,170.32	$1,170.35	$1,170.30