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	$153.35	4.217%	$159.8168	$159.82	$159.80	$159.80
Purchase #2	$175.47	9.495%	$192.1309	$192.13	$192.15	$192.10
Purchase #3	$240.68	13.433%	$273.0105	$273.01	$273.00	$273.00
Purchase #4	$90.78	6.631%	$96.7996	$96.80	$96.80	$96.80
Purchase #5	$99.43	9.170%	$108.5477	$108.55	$108.55	$108.50
Purchase #6	$80.90	3.611%	$83.8213	$83.82	$83.80	$83.80
Purchase #7	$227.77	13.611%	$258.7718	$258.77	$258.75	$258.80
7 purchase totals =	$1,068.38		$1,172.8986	$1,172.90	$1,172.85	$1,172.80