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	$24.81	12.308%	$27.8636	$27.86	$27.85	$27.90
Purchase #2	$138.63	6.476%	$147.6077	$147.61	$147.60	$147.60
Purchase #3	$71.39	9.342%	$78.0593	$78.06	$78.05	$78.10
Purchase #4	$50.55	9.396%	$55.2997	$55.30	$55.30	$55.30
Purchase #5	$216.65	10.807%	$240.0634	$240.06	$240.05	$240.10
Purchase #6	$136.64	5.435%	$144.0664	$144.07	$144.05	$144.10
Purchase #7	$122.84	3.523%	$127.1677	$127.17	$127.15	$127.20
7 purchase totals =	$761.51		$820.1278	$820.13	$820.05	$820.30