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	$194.27	6.766%	$207.4143	$207.41	$207.40	$207.40
Purchase #2	$132.38	9.395%	$144.8171	$144.82	$144.80	$144.80
Purchase #3	$74.68	11.775%	$83.4736	$83.47	$83.45	$83.50
Purchase #4	$40.29	9.620%	$44.1659	$44.17	$44.15	$44.20
Purchase #5	$40.28	10.565%	$44.5356	$44.54	$44.55	$44.50
Purchase #6	$152.60	10.622%	$168.8092	$168.81	$168.80	$168.80
Purchase #7	$98.28	13.112%	$111.1665	$111.17	$111.15	$111.20
7 purchase totals =	$732.78		$804.3822	$804.39	$804.30	$804.40