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	$156.29	6.394%	$166.2832	$166.28	$166.30	$166.30
Purchase #2	$145.97	9.248%	$159.4693	$159.47	$159.45	$159.50
Purchase #3	$74.62	4.671%	$78.1055	$78.11	$78.10	$78.10
Purchase #4	$57.77	7.797%	$62.2743	$62.27	$62.25	$62.30
Purchase #5	$243.69	4.759%	$255.2872	$255.29	$255.30	$255.30
Purchase #6	$13.96	13.680%	$15.8697	$15.87	$15.85	$15.90
Purchase #7	$93.37	3.160%	$96.3205	$96.32	$96.30	$96.30
7 purchase totals =	$785.67		$833.6097	$833.61	$833.55	$833.70