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	$52.79	5.270%	$55.572	$55.57	$55.55	$55.60
Purchase #2	$13.69	10.636%	$15.1461	$15.15	$15.15	$15.10
Purchase #3	$127.72	13.734%	$145.2611	$145.26	$145.25	$145.30
Purchase #4	$137.71	10.324%	$151.9272	$151.93	$151.95	$151.90
Purchase #5	$153.41	7.602%	$165.0722	$165.07	$165.05	$165.10
Purchase #6	$27.66	4.592%	$28.9301	$28.93	$28.95	$28.90
Purchase #7	$230.87	6.231%	$245.2555	$245.26	$245.25	$245.30
7 purchase totals =	$743.85		$807.1642	$807.17	$807.15	$807.20