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	$54.27	5.784%	$57.409	$57.41	$57.40	$57.40
Purchase #2	$59.89	9.862%	$65.7964	$65.80	$65.80	$65.80
Purchase #3	$224.60	10.198%	$247.5047	$247.50	$247.50	$247.50
Purchase #4	$122.61	4.260%	$127.8332	$127.83	$127.85	$127.80
Purchase #5	$83.97	9.269%	$91.7532	$91.75	$91.75	$91.80
Purchase #6	$230.90	8.486%	$250.4942	$250.49	$250.50	$250.50
Purchase #7	$118.63	6.714%	$126.5948	$126.59	$126.60	$126.60
7 purchase totals =	$894.87		$967.3855	$967.37	$967.40	$967.40