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	$77.47	12.702%	$87.3102	$87.31	$87.30	$87.30
Purchase #2	$48.88	7.334%	$52.4649	$52.46	$52.45	$52.50
Purchase #3	$34.52	11.600%	$38.5243	$38.52	$38.50	$38.50
Purchase #4	$174.32	9.523%	$190.9205	$190.92	$190.90	$190.90
Purchase #5	$47.68	10.217%	$52.5515	$52.55	$52.55	$52.60
Purchase #6	$10.54	11.364%	$11.7378	$11.74	$11.75	$11.70
Purchase #7	$178.71	9.198%	$195.1477	$195.15	$195.15	$195.10
7 purchase totals =	$572.12		$628.6569	$628.65	$628.60	$628.60