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	$46.83	9.224%	$51.1496	$51.15	$51.15	$51.10
Purchase #2	$150.51	11.371%	$167.6245	$167.62	$167.60	$167.60
Purchase #3	$238.29	7.393%	$255.9068	$255.91	$255.90	$255.90
Purchase #4	$203.25	10.350%	$224.2864	$224.29	$224.30	$224.30
Purchase #5	$151.37	5.826%	$160.1888	$160.19	$160.20	$160.20
Purchase #6	$100.30	6.661%	$106.981	$106.98	$107.00	$107.00
Purchase #7	$58.67	12.111%	$65.7755	$65.78	$65.80	$65.80
7 purchase totals =	$949.22		$1,031.9126	$1,031.92	$1,031.95	$1,031.90