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	$242.38	6.604%	$258.3868	$258.39	$258.40	$258.40
Purchase #2	$27.74	10.308%	$30.5994	$30.60	$30.60	$30.60
Purchase #3	$150.95	9.206%	$164.8465	$164.85	$164.85	$164.80
Purchase #4	$106.45	6.639%	$113.5172	$113.52	$113.50	$113.50
Purchase #5	$177.49	7.694%	$191.1461	$191.15	$191.15	$191.10
Purchase #6	$56.53	5.580%	$59.6844	$59.68	$59.70	$59.70
Purchase #7	$44.85	5.723%	$47.4168	$47.42	$47.40	$47.40
7 purchase totals =	$806.39		$865.5972	$865.61	$865.60	$865.50