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	$83.56	9.393%	$91.4088	$91.41	$91.40	$91.40
Purchase #2	$100.56	10.649%	$111.2686	$111.27	$111.25	$111.30
Purchase #3	$63.41	7.363%	$68.0789	$68.08	$68.10	$68.10
Purchase #4	$105.70	13.784%	$120.2697	$120.27	$120.25	$120.30
Purchase #5	$16.72	8.436%	$18.1305	$18.13	$18.15	$18.10
Purchase #6	$187.85	5.682%	$198.5236	$198.52	$198.50	$198.50
Purchase #7	$98.58	6.649%	$105.1346	$105.13	$105.15	$105.10
7 purchase totals =	$656.38		$712.8147	$712.81	$712.80	$712.80