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	$202.27	7.579%	$217.6	$217.60	$217.60	$217.60
Purchase #2	$98.98	12.663%	$111.5138	$111.51	$111.50	$111.50
Purchase #3	$57.26	11.419%	$63.7985	$63.80	$63.80	$63.80
Purchase #4	$111.96	8.197%	$121.1374	$121.14	$121.15	$121.10
Purchase #5	$108.73	7.224%	$116.5847	$116.58	$116.60	$116.60
Purchase #6	$206.89	11.232%	$230.1279	$230.13	$230.15	$230.10
Purchase #7	$120.32	6.762%	$128.456	$128.46	$128.45	$128.50
7 purchase totals =	$906.41		$989.2183	$989.22	$989.25	$989.20