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	$221.67	7.762%	$238.876	$238.88	$238.90	$238.90
Purchase #2	$34.62	12.839%	$39.0649	$39.06	$39.05	$39.10
Purchase #3	$13.69	11.797%	$15.305	$15.31	$15.30	$15.30
Purchase #4	$203.77	6.476%	$216.9661	$216.97	$216.95	$217.00
Purchase #5	$228.48	13.125%	$258.468	$258.47	$258.45	$258.50
Purchase #6	$19.43	3.639%	$20.1371	$20.14	$20.15	$20.10
Purchase #7	$39.57	5.146%	$41.6063	$41.61	$41.60	$41.60
7 purchase totals =	$761.23		$830.4234	$830.44	$830.40	$830.50