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	$173.34	11.284%	$192.8997	$192.90	$192.90	$192.90
Purchase #2	$220.48	5.714%	$233.0782	$233.08	$233.10	$233.10
Purchase #3	$206.52	7.852%	$222.736	$222.74	$222.75	$222.70
Purchase #4	$42.94	8.318%	$46.5117	$46.51	$46.50	$46.50
Purchase #5	$11.39	13.259%	$12.9002	$12.90	$12.90	$12.90
Purchase #6	$96.75	13.259%	$109.5781	$109.58	$109.60	$109.60
Purchase #7	$38.73	12.270%	$43.4822	$43.48	$43.50	$43.50
7 purchase totals =	$790.15		$861.1861	$861.19	$861.25	$861.20