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	$157.86	5.533%	$166.5944	$166.59	$166.60	$166.60
Purchase #2	$34.89	10.623%	$38.5964	$38.60	$38.60	$38.60
Purchase #3	$90.59	11.302%	$100.8285	$100.83	$100.85	$100.80
Purchase #4	$11.39	6.363%	$12.1147	$12.11	$12.10	$12.10
Purchase #5	$153.38	10.532%	$169.534	$169.53	$169.55	$169.50
Purchase #6	$237.64	7.373%	$255.1612	$255.16	$255.15	$255.20
Purchase #7	$22.68	3.238%	$23.4144	$23.41	$23.40	$23.40
7 purchase totals =	$708.43		$766.2436	$766.23	$766.25	$766.20