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	$130.90	8.379%	$141.8681	$141.87	$141.85	$141.90
Purchase #2	$70.52	10.114%	$77.6524	$77.65	$77.65	$77.70
Purchase #3	$103.47	7.494%	$111.224	$111.22	$111.20	$111.20
Purchase #4	$35.83	9.728%	$39.3155	$39.32	$39.30	$39.30
Purchase #5	$54.92	12.401%	$61.7306	$61.73	$61.75	$61.70
Purchase #6	$191.44	5.700%	$202.3521	$202.35	$202.35	$202.40
Purchase #7	$34.51	3.787%	$35.8169	$35.82	$35.80	$35.80
7 purchase totals =	$621.59		$669.9596	$669.96	$669.90	$670.00