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	$46.31	11.326%	$51.5551	$51.56	$51.55	$51.60
Purchase #2	$103.84	11.844%	$116.1388	$116.14	$116.15	$116.10
Purchase #3	$100.92	11.375%	$112.3997	$112.40	$112.40	$112.40
Purchase #4	$203.47	13.300%	$230.5315	$230.53	$230.55	$230.50
Purchase #5	$56.51	5.568%	$59.6565	$59.66	$59.65	$59.70
Purchase #6	$106.46	3.492%	$110.1776	$110.18	$110.20	$110.20
Purchase #7	$28.42	13.773%	$32.3343	$32.33	$32.35	$32.30
7 purchase totals =	$645.93		$712.7935	$712.80	$712.85	$712.80