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	$170.82	8.233%	$184.8836	$184.88	$184.90	$184.90
Purchase #2	$128.71	3.397%	$133.0823	$133.08	$133.10	$133.10
Purchase #3	$83.38	3.769%	$86.5226	$86.52	$86.50	$86.50
Purchase #4	$233.55	8.275%	$252.8763	$252.88	$252.90	$252.90
Purchase #5	$53.83	10.594%	$59.5328	$59.53	$59.55	$59.50
Purchase #6	$170.71	5.813%	$180.6334	$180.63	$180.65	$180.60
Purchase #7	$159.56	13.546%	$181.174	$181.17	$181.15	$181.20
7 purchase totals =	$1,000.56		$1,078.7050	$1,078.69	$1,078.75	$1,078.70