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	$205.92	12.421%	$231.4973	$231.50	$231.50	$231.50
Purchase #2	$53.32	10.653%	$59.0002	$59.00	$59.00	$59.00
Purchase #3	$226.28	3.244%	$233.6205	$233.62	$233.60	$233.60
Purchase #4	$123.51	7.767%	$133.103	$133.10	$133.10	$133.10
Purchase #5	$111.94	4.439%	$116.909	$116.91	$116.90	$116.90
Purchase #6	$36.88	10.325%	$40.6879	$40.69	$40.70	$40.70
Purchase #7	$235.90	4.205%	$245.8196	$245.82	$245.80	$245.80
7 purchase totals =	$993.75		$1,060.6375	$1,060.64	$1,060.60	$1,060.60