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	$249.78	11.767%	$279.1716	$279.17	$279.15	$279.20
Purchase #2	$63.48	3.677%	$65.8142	$65.81	$65.80	$65.80
Purchase #3	$31.98	5.113%	$33.6151	$33.62	$33.60	$33.60
Purchase #4	$165.98	9.443%	$181.6535	$181.65	$181.65	$181.70
Purchase #5	$125.41	9.354%	$137.1409	$137.14	$137.15	$137.10
Purchase #6	$248.66	9.149%	$271.4099	$271.41	$271.40	$271.40
Purchase #7	$56.85	13.418%	$64.4781	$64.48	$64.50	$64.50
7 purchase totals =	$942.14		$1,033.2833	$1,033.28	$1,033.25	$1,033.30