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	$56.38	6.403%	$59.99	$59.99	$60.00	$60.00
Purchase #2	$50.86	12.611%	$57.274	$57.27	$57.25	$57.30
Purchase #3	$132.50	7.562%	$142.5197	$142.52	$142.50	$142.50
Purchase #4	$228.35	10.410%	$252.1212	$252.12	$252.10	$252.10
Purchase #5	$148.51	3.579%	$153.8252	$153.83	$153.85	$153.80
Purchase #6	$99.36	12.659%	$111.938	$111.94	$111.95	$111.90
Purchase #7	$233.45	13.175%	$264.207	$264.21	$264.20	$264.20
7 purchase totals =	$949.41		$1,041.8751	$1,041.88	$1,041.85	$1,041.80