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	$37.47	3.586%	$38.8137	$38.81	$38.80	$38.80
Purchase #2	$22.30	13.587%	$25.3299	$25.33	$25.35	$25.30
Purchase #3	$154.96	11.172%	$172.2721	$172.27	$172.25	$172.30
Purchase #4	$126.26	3.525%	$130.7107	$130.71	$130.70	$130.70
Purchase #5	$6.96	5.493%	$7.3423	$7.34	$7.35	$7.30
Purchase #6	$116.82	9.765%	$128.2275	$128.23	$128.25	$128.20
Purchase #7	$123.40	3.404%	$127.6005	$127.60	$127.60	$127.60
7 purchase totals =	$588.17		$630.2967	$630.29	$630.30	$630.20