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	$32.43	12.583%	$36.5107	$36.51	$36.50	$36.50
Purchase #2	$233.34	10.747%	$258.417	$258.42	$258.40	$258.40
Purchase #3	$171.25	10.278%	$188.8511	$188.85	$188.85	$188.90
Purchase #4	$116.47	13.385%	$132.0595	$132.06	$132.05	$132.10
Purchase #5	$144.89	4.599%	$151.5535	$151.55	$151.55	$151.60
Purchase #6	$12.31	4.185%	$12.8252	$12.83	$12.85	$12.80
Purchase #7	$214.59	7.168%	$229.9718	$229.97	$229.95	$230.00
7 purchase totals =	$925.28		$1,010.1888	$1,010.19	$1,010.15	$1,010.30