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	$230.38	8.435%	$249.8126	$249.81	$249.80	$249.80
Purchase #2	$146.58	11.255%	$163.0776	$163.08	$163.10	$163.10
Purchase #3	$67.78	5.663%	$71.6184	$71.62	$71.60	$71.60
Purchase #4	$103.37	5.728%	$109.291	$109.29	$109.30	$109.30
Purchase #5	$82.38	9.134%	$89.9046	$89.90	$89.90	$89.90
Purchase #6	$93.84	6.303%	$99.7547	$99.75	$99.75	$99.80
Purchase #7	$123.83	7.172%	$132.7111	$132.71	$132.70	$132.70
7 purchase totals =	$848.16		$916.1700	$916.16	$916.15	$916.20