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	$6.76	8.519%	$7.3359	$7.34	$7.35	$7.30
Purchase #2	$63.78	12.543%	$71.7799	$71.78	$71.80	$71.80
Purchase #3	$243.64	6.358%	$259.1306	$259.13	$259.15	$259.10
Purchase #4	$41.49	13.321%	$47.0169	$47.02	$47.00	$47.00
Purchase #5	$105.52	5.406%	$111.2244	$111.22	$111.20	$111.20
Purchase #6	$17.87	9.578%	$19.5816	$19.58	$19.60	$19.60
Purchase #7	$81.91	4.108%	$85.2749	$85.27	$85.25	$85.30
7 purchase totals =	$560.97		$601.3442	$601.34	$601.35	$601.30