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	$37.77	8.177%	$40.8585	$40.86	$40.85	$40.90
Purchase #2	$65.44	7.672%	$70.4606	$70.46	$70.45	$70.50
Purchase #3	$9.67	11.737%	$10.805	$10.81	$10.80	$10.80
Purchase #4	$92.87	8.681%	$100.932	$100.93	$100.95	$100.90
Purchase #5	$54.35	8.297%	$58.8594	$58.86	$58.85	$58.90
Purchase #6	$158.91	12.309%	$178.4702	$178.47	$178.45	$178.50
Purchase #7	$49.52	13.463%	$56.1869	$56.19	$56.20	$56.20
7 purchase totals =	$468.53		$516.5726	$516.58	$516.55	$516.70