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	$19.69	5.490%	$20.771	$20.77	$20.75	$20.80
Purchase #2	$143.84	10.260%	$158.598	$158.60	$158.60	$158.60
Purchase #3	$215.46	6.180%	$228.7754	$228.78	$228.80	$228.80
Purchase #4	$27.58	12.862%	$31.1273	$31.13	$31.15	$31.10
Purchase #5	$129.36	7.548%	$139.1241	$139.12	$139.10	$139.10
Purchase #6	$61.51	8.675%	$66.846	$66.85	$66.85	$66.80
Purchase #7	$25.85	10.575%	$28.5836	$28.58	$28.60	$28.60
7 purchase totals =	$623.29		$673.8254	$673.83	$673.85	$673.80