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	$227.30	5.595%	$240.0174	$240.02	$240.00	$240.00
Purchase #2	$116.38	9.270%	$127.1684	$127.17	$127.15	$127.20
Purchase #3	$101.51	9.854%	$111.5128	$111.51	$111.50	$111.50
Purchase #4	$29.93	7.178%	$32.0784	$32.08	$32.10	$32.10
Purchase #5	$28.74	7.496%	$30.8944	$30.89	$30.90	$30.90
Purchase #6	$53.35	13.487%	$60.5453	$60.55	$60.55	$60.50
Purchase #7	$113.91	12.202%	$127.8093	$127.81	$127.80	$127.80
7 purchase totals =	$671.12		$730.0260	$730.03	$730.00	$730.00