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	$48.37	11.656%	$54.008	$54.01	$54.00	$54.00
Purchase #2	$139.45	5.127%	$146.5996	$146.60	$146.60	$146.60
Purchase #3	$50.29	6.493%	$53.5553	$53.56	$53.55	$53.60
Purchase #4	$221.90	4.162%	$231.1355	$231.14	$231.15	$231.10
Purchase #5	$36.81	10.127%	$40.5377	$40.54	$40.55	$40.50
Purchase #6	$110.69	5.227%	$116.4758	$116.48	$116.50	$116.50
Purchase #7	$37.63	12.792%	$42.4436	$42.44	$42.45	$42.40
7 purchase totals =	$645.14		$684.7555	$684.77	$684.80	$684.70