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	$83.99	5.508%	$88.6162	$88.62	$88.60	$88.60
Purchase #2	$115.89	9.725%	$127.1603	$127.16	$127.15	$127.20
Purchase #3	$159.69	3.332%	$165.0109	$165.01	$165.00	$165.00
Purchase #4	$138.65	8.372%	$150.2578	$150.26	$150.25	$150.30
Purchase #5	$206.96	11.357%	$230.4644	$230.46	$230.45	$230.50
Purchase #6	$65.54	7.443%	$70.4181	$70.42	$70.40	$70.40
Purchase #7	$78.68	13.280%	$89.1287	$89.13	$89.15	$89.10
7 purchase totals =	$849.40		$921.0564	$921.06	$921.00	$921.10