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	$35.52	13.389%	$40.2758	$40.28	$40.30	$40.30
Purchase #2	$24.29	10.581%	$26.8601	$26.86	$26.85	$26.90
Purchase #3	$54.92	3.570%	$56.8806	$56.88	$56.90	$56.90
Purchase #4	$36.36	12.375%	$40.8596	$40.86	$40.85	$40.90
Purchase #5	$81.78	11.683%	$91.3344	$91.33	$91.35	$91.30
Purchase #6	$214.98	7.255%	$230.5768	$230.58	$230.60	$230.60
Purchase #7	$48.80	9.251%	$53.3145	$53.31	$53.30	$53.30
7 purchase totals =	$496.65		$540.1018	$540.10	$540.15	$540.20