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	$67.48	11.613%	$75.3165	$75.32	$75.30	$75.30
Purchase #2	$250.94	9.823%	$275.5898	$275.59	$275.60	$275.60
Purchase #3	$214.43	12.506%	$241.2466	$241.25	$241.25	$241.20
Purchase #4	$17.87	12.692%	$20.1381	$20.14	$20.15	$20.10
Purchase #5	$28.83	5.795%	$30.5007	$30.50	$30.50	$30.50
Purchase #6	$149.88	9.845%	$164.6357	$164.64	$164.65	$164.60
Purchase #7	$176.40	10.503%	$194.9273	$194.93	$194.95	$194.90
7 purchase totals =	$905.83		$1,002.3547	$1,002.37	$1,002.40	$1,002.20