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	$137.76	5.866%	$145.841	$145.84	$145.85	$145.80
Purchase #2	$127.52	10.838%	$141.3406	$141.34	$141.35	$141.30
Purchase #3	$131.35	10.598%	$145.2705	$145.27	$145.25	$145.30
Purchase #4	$30.60	4.739%	$32.0501	$32.05	$32.05	$32.10
Purchase #5	$156.61	10.347%	$172.8144	$172.81	$172.80	$172.80
Purchase #6	$126.31	8.592%	$137.1626	$137.16	$137.15	$137.20
Purchase #7	$67.26	5.549%	$70.9923	$70.99	$71.00	$71.00
7 purchase totals =	$777.41		$845.4715	$845.46	$845.45	$845.50