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	$190.72	9.176%	$208.2205	$208.22	$208.20	$208.20
Purchase #2	$28.35	10.250%	$31.2559	$31.26	$31.25	$31.30
Purchase #3	$204.50	9.189%	$223.2915	$223.29	$223.30	$223.30
Purchase #4	$12.49	3.196%	$12.8892	$12.89	$12.90	$12.90
Purchase #5	$37.46	5.641%	$39.5731	$39.57	$39.55	$39.60
Purchase #6	$99.37	11.771%	$111.0668	$111.07	$111.05	$111.10
Purchase #7	$176.65	10.208%	$194.6824	$194.68	$194.70	$194.70
7 purchase totals =	$749.54		$820.9794	$820.98	$820.95	$821.10