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	$181.29	3.307%	$187.2853	$187.29	$187.30	$187.30
Purchase #2	$79.62	3.643%	$82.5206	$82.52	$82.50	$82.50
Purchase #3	$57.52	6.721%	$61.3859	$61.39	$61.40	$61.40
Purchase #4	$122.68	13.649%	$139.4246	$139.42	$139.40	$139.40
Purchase #5	$37.46	10.609%	$41.4341	$41.43	$41.45	$41.40
Purchase #6	$97.60	9.198%	$106.5772	$106.58	$106.60	$106.60
Purchase #7	$25.43	10.748%	$28.1632	$28.16	$28.15	$28.20
7 purchase totals =	$601.60		$646.7909	$646.79	$646.80	$646.80