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	$11.27	12.796%	$12.7121	$12.71	$12.70	$12.70
Purchase #2	$208.48	10.429%	$230.2224	$230.22	$230.20	$230.20
Purchase #3	$180.69	8.641%	$196.3034	$196.30	$196.30	$196.30
Purchase #4	$156.57	10.337%	$172.7546	$172.75	$172.75	$172.80
Purchase #5	$96.32	6.657%	$102.732	$102.73	$102.75	$102.70
Purchase #6	$234.55	11.492%	$261.5045	$261.50	$261.50	$261.50
Purchase #7	$91.51	11.670%	$102.1892	$102.19	$102.20	$102.20
7 purchase totals =	$979.39		$1,078.4182	$1,078.40	$1,078.40	$1,078.40