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	$226.47	3.213%	$233.7465	$233.75	$233.75	$233.70
Purchase #2	$74.71	4.682%	$78.2079	$78.21	$78.20	$78.20
Purchase #3	$141.46	9.608%	$155.0515	$155.05	$155.05	$155.10
Purchase #4	$126.39	10.772%	$140.0047	$140.00	$140.00	$140.00
Purchase #5	$101.39	10.172%	$111.7034	$111.70	$111.70	$111.70
Purchase #6	$225.52	12.536%	$253.7912	$253.79	$253.80	$253.80
Purchase #7	$122.65	11.147%	$136.3218	$136.32	$136.30	$136.30
7 purchase totals =	$1,018.59		$1,108.8270	$1,108.82	$1,108.80	$1,108.80