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	$229.81	3.677%	$238.2601	$238.26	$238.25	$238.30
Purchase #2	$118.39	10.773%	$131.1442	$131.14	$131.15	$131.10
Purchase #3	$225.46	11.584%	$251.5773	$251.58	$251.60	$251.60
Purchase #4	$134.41	13.651%	$152.7583	$152.76	$152.75	$152.80
Purchase #5	$39.67	4.865%	$41.5999	$41.60	$41.60	$41.60
Purchase #6	$123.68	12.246%	$138.8259	$138.83	$138.85	$138.80
Purchase #7	$38.62	4.157%	$40.2254	$40.23	$40.25	$40.20
7 purchase totals =	$910.04		$994.3911	$994.40	$994.45	$994.40