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	$39.25	7.320%	$42.1231	$42.12	$42.10	$42.10
Purchase #2	$161.54	9.296%	$176.5568	$176.56	$176.55	$176.60
Purchase #3	$246.95	10.243%	$272.2451	$272.25	$272.25	$272.20
Purchase #4	$62.95	5.824%	$66.6162	$66.62	$66.60	$66.60
Purchase #5	$56.35	5.689%	$59.5558	$59.56	$59.55	$59.60
Purchase #6	$25.50	12.569%	$28.7051	$28.71	$28.70	$28.70
Purchase #7	$48.30	13.692%	$54.9132	$54.91	$54.90	$54.90
7 purchase totals =	$640.84		$700.7153	$700.73	$700.65	$700.70