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	$105.40	4.218%	$109.8458	$109.85	$109.85	$109.80
Purchase #2	$127.80	12.146%	$143.3226	$143.32	$143.30	$143.30
Purchase #3	$9.53	6.651%	$10.1638	$10.16	$10.15	$10.20
Purchase #4	$173.71	11.405%	$193.5216	$193.52	$193.50	$193.50
Purchase #5	$134.50	13.167%	$152.2096	$152.21	$152.20	$152.20
Purchase #6	$127.33	5.744%	$134.6438	$134.64	$134.65	$134.60
Purchase #7	$233.68	6.697%	$249.3295	$249.33	$249.35	$249.30
7 purchase totals =	$911.95		$993.0367	$993.03	$993.00	$992.90