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	$28.55	13.581%	$32.4274	$32.43	$32.45	$32.40
Purchase #2	$124.35	6.205%	$132.0659	$132.07	$132.05	$132.10
Purchase #3	$51.45	10.199%	$56.6974	$56.70	$56.70	$56.70
Purchase #4	$90.47	10.861%	$100.2959	$100.30	$100.30	$100.30
Purchase #5	$89.28	10.488%	$98.6437	$98.64	$98.65	$98.60
Purchase #6	$184.25	7.404%	$197.8919	$197.89	$197.90	$197.90
Purchase #7	$207.86	11.553%	$231.8741	$231.87	$231.85	$231.90
7 purchase totals =	$776.21		$849.8963	$849.90	$849.90	$849.90