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	$132.59	5.448%	$139.8135	$139.81	$139.80	$139.80
Purchase #2	$202.65	13.530%	$230.0685	$230.07	$230.05	$230.10
Purchase #3	$159.79	13.620%	$181.5534	$181.55	$181.55	$181.60
Purchase #4	$77.31	12.864%	$87.2552	$87.26	$87.25	$87.30
Purchase #5	$72.44	13.588%	$82.2831	$82.28	$82.30	$82.30
Purchase #6	$82.39	12.472%	$92.6657	$92.67	$92.65	$92.70
Purchase #7	$74.77	9.770%	$82.075	$82.08	$82.10	$82.10
7 purchase totals =	$801.94		$895.7144	$895.72	$895.70	$895.90