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	$116.30	12.819%	$131.2085	$131.21	$131.20	$131.20
Purchase #2	$51.54	8.277%	$55.806	$55.81	$55.80	$55.80
Purchase #3	$32.92	13.621%	$37.404	$37.40	$37.40	$37.40
Purchase #4	$22.57	7.249%	$24.2061	$24.21	$24.20	$24.20
Purchase #5	$48.59	12.153%	$54.4951	$54.50	$54.50	$54.50
Purchase #6	$159.99	9.640%	$175.413	$175.41	$175.40	$175.40
Purchase #7	$143.62	6.510%	$152.9697	$152.97	$152.95	$153.00
7 purchase totals =	$575.53		$631.5024	$631.51	$631.45	$631.50