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	$24.51	6.690%	$26.1497	$26.15	$26.15	$26.10
Purchase #2	$78.58	5.277%	$82.7267	$82.73	$82.75	$82.70
Purchase #3	$80.34	11.427%	$89.5205	$89.52	$89.50	$89.50
Purchase #4	$178.61	6.612%	$190.4197	$190.42	$190.40	$190.40
Purchase #5	$33.69	3.608%	$34.9055	$34.91	$34.90	$34.90
Purchase #6	$234.51	7.867%	$252.9589	$252.96	$252.95	$253.00
Purchase #7	$104.42	9.111%	$113.9337	$113.93	$113.95	$113.90
7 purchase totals =	$734.66		$790.6147	$790.62	$790.60	$790.50