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	$32.42	12.225%	$36.3833	$36.38	$36.40	$36.40
Purchase #2	$90.60	11.188%	$100.7363	$100.74	$100.75	$100.70
Purchase #3	$136.92	6.288%	$145.5295	$145.53	$145.55	$145.50
Purchase #4	$204.40	11.798%	$228.5151	$228.52	$228.50	$228.50
Purchase #5	$242.93	4.827%	$254.6562	$254.66	$254.65	$254.70
Purchase #6	$68.28	9.632%	$74.8567	$74.86	$74.85	$74.90
Purchase #7	$227.83	11.545%	$254.133	$254.13	$254.15	$254.10
7 purchase totals =	$1,003.38		$1,094.8101	$1,094.82	$1,094.85	$1,094.80