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	$55.26	6.819%	$59.0282	$59.03	$59.05	$59.00
Purchase #2	$47.32	12.321%	$53.1503	$53.15	$53.15	$53.20
Purchase #3	$147.35	13.498%	$167.2393	$167.24	$167.25	$167.20
Purchase #4	$173.42	7.672%	$186.7248	$186.72	$186.70	$186.70
Purchase #5	$17.75	10.457%	$19.6061	$19.61	$19.60	$19.60
Purchase #6	$125.89	5.688%	$133.0506	$133.05	$133.05	$133.10
Purchase #7	$92.28	8.787%	$100.3886	$100.39	$100.40	$100.40
7 purchase totals =	$659.27		$719.1879	$719.19	$719.20	$719.20