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	$20.30	4.694%	$21.2529	$21.25	$21.25	$21.30
Purchase #2	$51.89	6.217%	$55.116	$55.12	$55.10	$55.10
Purchase #3	$158.56	3.248%	$163.71	$163.71	$163.70	$163.70
Purchase #4	$57.26	3.306%	$59.153	$59.15	$59.15	$59.20
Purchase #5	$19.83	9.364%	$21.6869	$21.69	$21.70	$21.70
Purchase #6	$148.76	10.309%	$164.0957	$164.10	$164.10	$164.10
Purchase #7	$11.90	3.301%	$12.2928	$12.29	$12.30	$12.30
7 purchase totals =	$468.50		$497.3073	$497.31	$497.30	$497.40