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	$246.69	12.608%	$277.7927	$277.79	$277.80	$277.80
Purchase #2	$104.91	6.303%	$111.5225	$111.52	$111.50	$111.50
Purchase #3	$132.75	11.489%	$148.0016	$148.00	$148.00	$148.00
Purchase #4	$192.95	5.788%	$204.1179	$204.12	$204.10	$204.10
Purchase #5	$161.56	8.483%	$175.2651	$175.27	$175.25	$175.30
Purchase #6	$9.59	4.839%	$10.0541	$10.05	$10.05	$10.10
Purchase #7	$244.48	10.391%	$269.8839	$269.88	$269.90	$269.90
7 purchase totals =	$1,092.93		$1,196.6378	$1,196.63	$1,196.60	$1,196.70