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	$46.97	6.262%	$49.9113	$49.91	$49.90	$49.90
Purchase #2	$126.43	13.191%	$143.1074	$143.11	$143.10	$143.10
Purchase #3	$167.30	6.705%	$178.5175	$178.52	$178.50	$178.50
Purchase #4	$104.25	7.140%	$111.6935	$111.69	$111.70	$111.70
Purchase #5	$216.67	5.148%	$227.8242	$227.82	$227.80	$227.80
Purchase #6	$226.91	9.294%	$247.999	$248.00	$248.00	$248.00
Purchase #7	$103.87	3.806%	$107.8233	$107.82	$107.80	$107.80
7 purchase totals =	$992.40		$1,066.8762	$1,066.87	$1,066.80	$1,066.80