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	$26.45	10.728%	$29.2876	$29.29	$29.30	$29.30
Purchase #2	$89.30	12.643%	$100.5902	$100.59	$100.60	$100.60
Purchase #3	$72.75	13.615%	$82.6549	$82.65	$82.65	$82.70
Purchase #4	$17.28	9.109%	$18.854	$18.85	$18.85	$18.90
Purchase #5	$191.84	13.185%	$217.1341	$217.13	$217.15	$217.10
Purchase #6	$67.27	5.230%	$70.7882	$70.79	$70.80	$70.80
Purchase #7	$7.94	11.107%	$8.8219	$8.82	$8.80	$8.80
7 purchase totals =	$472.83		$528.1309	$528.12	$528.15	$528.20