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	$245.56	13.692%	$279.1821	$279.18	$279.20	$279.20
Purchase #2	$56.30	3.337%	$58.1787	$58.18	$58.20	$58.20
Purchase #3	$197.72	6.345%	$210.2653	$210.27	$210.25	$210.30
Purchase #4	$224.26	7.258%	$240.5368	$240.54	$240.55	$240.50
Purchase #5	$41.39	9.572%	$45.3519	$45.35	$45.35	$45.40
Purchase #6	$124.65	6.121%	$132.2798	$132.28	$132.30	$132.30
Purchase #7	$100.88	10.843%	$111.8184	$111.82	$111.80	$111.80
7 purchase totals =	$990.76		$1,077.6130	$1,077.62	$1,077.65	$1,077.70