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	$220.98	12.637%	$248.9052	$248.91	$248.90	$248.90
Purchase #2	$129.61	11.856%	$144.9766	$144.98	$145.00	$145.00
Purchase #3	$13.60	3.835%	$14.1216	$14.12	$14.10	$14.10
Purchase #4	$49.28	10.227%	$54.3199	$54.32	$54.30	$54.30
Purchase #5	$12.98	9.685%	$14.2371	$14.24	$14.25	$14.20
Purchase #6	$111.35	11.717%	$124.3969	$124.40	$124.40	$124.40
Purchase #7	$40.72	4.240%	$42.4465	$42.45	$42.45	$42.40
7 purchase totals =	$578.52		$643.4038	$643.42	$643.40	$643.30