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	$87.84	13.218%	$99.4507	$99.45	$99.45	$99.50
Purchase #2	$14.67	3.493%	$15.1824	$15.18	$15.20	$15.20
Purchase #3	$147.28	8.140%	$159.2686	$159.27	$159.25	$159.30
Purchase #4	$138.46	6.523%	$147.4917	$147.49	$147.50	$147.50
Purchase #5	$52.88	12.264%	$59.3652	$59.37	$59.35	$59.40
Purchase #6	$220.51	9.506%	$241.4717	$241.47	$241.45	$241.50
Purchase #7	$168.64	5.782%	$178.3908	$178.39	$178.40	$178.40
7 purchase totals =	$830.28		$900.6211	$900.62	$900.60	$900.80