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	$68.99	12.381%	$77.5317	$77.53	$77.55	$77.50
Purchase #2	$171.26	12.554%	$192.76	$192.76	$192.75	$192.80
Purchase #3	$15.58	12.469%	$17.5227	$17.52	$17.50	$17.50
Purchase #4	$113.99	12.707%	$128.4747	$128.47	$128.45	$128.50
Purchase #5	$39.27	6.753%	$41.9219	$41.92	$41.90	$41.90
Purchase #6	$20.82	3.433%	$21.5348	$21.53	$21.55	$21.50
Purchase #7	$141.56	4.145%	$147.4277	$147.43	$147.45	$147.40
7 purchase totals =	$571.47		$627.1735	$627.16	$627.15	$627.10