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	$149.35	5.210%	$157.1311	$157.13	$157.15	$157.10
Purchase #2	$75.49	9.601%	$82.7378	$82.74	$82.75	$82.70
Purchase #3	$196.48	7.852%	$211.9076	$211.91	$211.90	$211.90
Purchase #4	$153.45	9.117%	$167.44	$167.44	$167.45	$167.40
Purchase #5	$67.44	10.590%	$74.5819	$74.58	$74.60	$74.60
Purchase #6	$80.39	12.535%	$90.4669	$90.47	$90.45	$90.50
Purchase #7	$17.96	12.160%	$20.1439	$20.14	$20.15	$20.10
7 purchase totals =	$740.56		$804.4092	$804.41	$804.45	$804.30