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	$68.85	3.583%	$71.3169	$71.32	$71.30	$71.30
Purchase #2	$238.72	5.768%	$252.4894	$252.49	$252.50	$252.50
Purchase #3	$247.63	8.409%	$268.4532	$268.45	$268.45	$268.50
Purchase #4	$135.62	4.540%	$141.7771	$141.78	$141.80	$141.80
Purchase #5	$107.45	3.439%	$111.1452	$111.15	$111.15	$111.10
Purchase #6	$48.43	3.831%	$50.2854	$50.29	$50.30	$50.30
Purchase #7	$32.80	10.655%	$36.2948	$36.29	$36.30	$36.30
7 purchase totals =	$879.50		$931.7620	$931.77	$931.80	$931.80