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	$241.40	12.780%	$272.2509	$272.25	$272.25	$272.30
Purchase #2	$54.88	10.500%	$60.6424	$60.64	$60.65	$60.60
Purchase #3	$85.68	6.712%	$91.4308	$91.43	$91.45	$91.40
Purchase #4	$10.37	4.717%	$10.8592	$10.86	$10.85	$10.90
Purchase #5	$156.75	6.627%	$167.1378	$167.14	$167.15	$167.10
Purchase #6	$122.85	3.819%	$127.5416	$127.54	$127.55	$127.50
Purchase #7	$114.98	11.458%	$128.1544	$128.15	$128.15	$128.20
7 purchase totals =	$786.91		$858.0171	$858.01	$858.05	$858.00