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	$225.87	6.827%	$241.2901	$241.29	$241.30	$241.30
Purchase #2	$34.90	7.189%	$37.409	$37.41	$37.40	$37.40
Purchase #3	$205.82	5.129%	$216.3765	$216.38	$216.40	$216.40
Purchase #4	$139.83	10.603%	$154.6562	$154.66	$154.65	$154.70
Purchase #5	$28.60	13.786%	$32.5428	$32.54	$32.55	$32.50
Purchase #6	$110.78	8.267%	$119.9382	$119.94	$119.95	$119.90
Purchase #7	$145.94	4.137%	$151.9775	$151.98	$152.00	$152.00
7 purchase totals =	$891.74		$954.1903	$954.20	$954.25	$954.20