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	$10.58	9.434%	$11.5781	$11.58	$11.60	$11.60
Purchase #2	$96.49	8.227%	$104.4282	$104.43	$104.45	$104.40
Purchase #3	$81.78	7.722%	$88.0951	$88.10	$88.10	$88.10
Purchase #4	$111.33	11.798%	$124.4647	$124.46	$124.45	$124.50
Purchase #5	$91.62	12.811%	$103.3574	$103.36	$103.35	$103.40
Purchase #6	$55.77	8.147%	$60.3136	$60.31	$60.30	$60.30
Purchase #7	$145.32	9.173%	$158.6502	$158.65	$158.65	$158.70
7 purchase totals =	$592.89		$650.8873	$650.89	$650.90	$651.00