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	$90.51	10.812%	$100.2959	$100.30	$100.30	$100.30
Purchase #2	$230.26	10.583%	$254.6284	$254.63	$254.65	$254.60
Purchase #3	$233.27	9.328%	$255.0294	$255.03	$255.05	$255.00
Purchase #4	$36.73	4.742%	$38.4717	$38.47	$38.45	$38.50
Purchase #5	$186.76	12.678%	$210.4374	$210.44	$210.45	$210.40
Purchase #6	$24.60	4.411%	$25.6851	$25.69	$25.70	$25.70
Purchase #7	$11.77	4.470%	$12.2961	$12.30	$12.30	$12.30
7 purchase totals =	$813.90		$896.8440	$896.86	$896.90	$896.80