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	$61.50	10.576%	$68.0042	$68.00	$68.00	$68.00
Purchase #2	$77.90	10.259%	$85.8918	$85.89	$85.90	$85.90
Purchase #3	$40.75	10.559%	$45.0528	$45.05	$45.05	$45.10
Purchase #4	$217.73	3.862%	$226.1387	$226.14	$226.15	$226.10
Purchase #5	$38.45	10.580%	$42.518	$42.52	$42.50	$42.50
Purchase #6	$38.55	12.397%	$43.329	$43.33	$43.35	$43.30
Purchase #7	$76.66	11.632%	$85.5771	$85.58	$85.60	$85.60
7 purchase totals =	$551.54		$596.5116	$596.51	$596.55	$596.50