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	$66.72	12.307%	$74.9312	$74.93	$74.95	$74.90
Purchase #2	$17.51	5.301%	$18.4382	$18.44	$18.45	$18.40
Purchase #3	$187.51	13.103%	$212.0794	$212.08	$212.10	$212.10
Purchase #4	$54.34	6.161%	$57.6879	$57.69	$57.70	$57.70
Purchase #5	$178.31	12.458%	$200.5239	$200.52	$200.50	$200.50
Purchase #6	$41.25	5.595%	$43.5579	$43.56	$43.55	$43.60
Purchase #7	$118.61	13.502%	$134.6247	$134.62	$134.60	$134.60
7 purchase totals =	$664.25		$741.8432	$741.84	$741.85	$741.80