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	$9.27	13.493%	$10.5208	$10.52	$10.50	$10.50
Purchase #2	$126.59	13.662%	$143.8847	$143.88	$143.90	$143.90
Purchase #3	$75.35	10.129%	$82.9822	$82.98	$83.00	$83.00
Purchase #4	$122.85	4.309%	$128.1436	$128.14	$128.15	$128.10
Purchase #5	$236.77	11.282%	$263.4824	$263.48	$263.50	$263.50
Purchase #6	$174.25	3.351%	$180.0891	$180.09	$180.10	$180.10
Purchase #7	$244.41	4.385%	$255.1274	$255.13	$255.15	$255.10
7 purchase totals =	$989.49		$1,064.2302	$1,064.22	$1,064.30	$1,064.20