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	$34.40	7.271%	$36.9012	$36.90	$36.90	$36.90
Purchase #2	$119.34	6.456%	$127.0446	$127.04	$127.05	$127.00
Purchase #3	$144.74	6.279%	$153.8282	$153.83	$153.85	$153.80
Purchase #4	$181.85	9.522%	$199.1658	$199.17	$199.15	$199.20
Purchase #5	$90.53	7.323%	$97.1595	$97.16	$97.15	$97.20
Purchase #6	$144.82	7.451%	$155.6105	$155.61	$155.60	$155.60
Purchase #7	$50.26	12.270%	$56.4269	$56.43	$56.45	$56.40
7 purchase totals =	$765.94		$826.1367	$826.14	$826.15	$826.10