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	$81.52	10.548%	$90.1187	$90.12	$90.10	$90.10
Purchase #2	$79.35	10.453%	$87.6445	$87.64	$87.65	$87.60
Purchase #3	$11.41	13.338%	$12.9319	$12.93	$12.95	$12.90
Purchase #4	$174.90	3.821%	$181.5829	$181.58	$181.60	$181.60
Purchase #5	$42.39	6.743%	$45.2484	$45.25	$45.25	$45.20
Purchase #6	$172.87	10.754%	$191.4604	$191.46	$191.45	$191.50
Purchase #7	$29.36	7.535%	$31.5723	$31.57	$31.55	$31.60
7 purchase totals =	$591.80		$640.5591	$640.55	$640.55	$640.50