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	$244.76	5.529%	$258.2928	$258.29	$258.30	$258.30
Purchase #2	$184.46	8.398%	$199.951	$199.95	$199.95	$200.00
Purchase #3	$75.87	10.321%	$83.7005	$83.70	$83.70	$83.70
Purchase #4	$134.54	13.413%	$152.5859	$152.59	$152.60	$152.60
Purchase #5	$80.63	3.193%	$83.2045	$83.20	$83.20	$83.20
Purchase #6	$105.69	5.684%	$111.6974	$111.70	$111.70	$111.70
Purchase #7	$168.89	12.792%	$190.4944	$190.49	$190.50	$190.50
7 purchase totals =	$994.84		$1,079.9265	$1,079.92	$1,079.95	$1,080.00