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	$35.44	11.689%	$39.5826	$39.58	$39.60	$39.60
Purchase #2	$25.96	6.595%	$27.6721	$27.67	$27.65	$27.70
Purchase #3	$88.91	12.647%	$100.1544	$100.15	$100.15	$100.20
Purchase #4	$97.28	6.828%	$103.9223	$103.92	$103.90	$103.90
Purchase #5	$129.57	10.650%	$143.3692	$143.37	$143.35	$143.40
Purchase #6	$205.70	11.454%	$229.2609	$229.26	$229.25	$229.30
Purchase #7	$198.37	13.485%	$225.1202	$225.12	$225.10	$225.10
7 purchase totals =	$781.23		$869.0817	$869.07	$869.00	$869.20