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	$170.80	9.670%	$187.3164	$187.32	$187.30	$187.30
Purchase #2	$93.31	13.206%	$105.6325	$105.63	$105.65	$105.60
Purchase #3	$59.62	6.191%	$63.3111	$63.31	$63.30	$63.30
Purchase #4	$9.99	12.431%	$11.2319	$11.23	$11.25	$11.20
Purchase #5	$99.92	5.665%	$105.5805	$105.58	$105.60	$105.60
Purchase #6	$34.56	8.194%	$37.3918	$37.39	$37.40	$37.40
Purchase #7	$136.29	6.210%	$144.7536	$144.75	$144.75	$144.80
7 purchase totals =	$604.49		$655.2178	$655.21	$655.25	$655.20