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	$68.80	5.734%	$72.745	$72.75	$72.75	$72.70
Purchase #2	$89.78	13.263%	$101.6875	$101.69	$101.70	$101.70
Purchase #3	$105.57	5.448%	$111.3215	$111.32	$111.30	$111.30
Purchase #4	$202.98	13.719%	$230.8268	$230.83	$230.85	$230.80
Purchase #5	$226.91	8.506%	$246.211	$246.21	$246.20	$246.20
Purchase #6	$58.70	4.804%	$61.5199	$61.52	$61.50	$61.50
Purchase #7	$136.52	12.503%	$153.5891	$153.59	$153.60	$153.60
7 purchase totals =	$889.26		$977.9008	$977.91	$977.90	$977.80