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	$5.49	11.754%	$6.1353	$6.14	$6.15	$6.10
Purchase #2	$151.58	10.794%	$167.9415	$167.94	$167.95	$167.90
Purchase #3	$216.55	5.331%	$228.0943	$228.09	$228.10	$228.10
Purchase #4	$227.98	4.611%	$238.4922	$238.49	$238.50	$238.50
Purchase #5	$81.75	9.836%	$89.7909	$89.79	$89.80	$89.80
Purchase #6	$247.83	7.442%	$266.2735	$266.27	$266.25	$266.30
Purchase #7	$10.64	9.244%	$11.6236	$11.62	$11.60	$11.60
7 purchase totals =	$941.82		$1,008.3513	$1,008.34	$1,008.35	$1,008.30