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	$156.77	13.548%	$178.0092	$178.01	$178.00	$178.00
Purchase #2	$38.61	12.698%	$43.5127	$43.51	$43.50	$43.50
Purchase #3	$178.66	10.238%	$196.9512	$196.95	$196.95	$197.00
Purchase #4	$101.38	10.167%	$111.6873	$111.69	$111.70	$111.70
Purchase #5	$24.73	9.769%	$27.1459	$27.15	$27.15	$27.10
Purchase #6	$87.51	10.170%	$96.4098	$96.41	$96.40	$96.40
Purchase #7	$157.28	12.268%	$176.5751	$176.58	$176.60	$176.60
7 purchase totals =	$744.94		$830.2912	$830.30	$830.30	$830.30