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	$6.64	9.679%	$7.2827	$7.28	$7.30	$7.30
Purchase #2	$54.65	12.624%	$61.549	$61.55	$61.55	$61.50
Purchase #3	$182.27	12.734%	$205.4803	$205.48	$205.50	$205.50
Purchase #4	$68.59	3.142%	$70.7451	$70.75	$70.75	$70.70
Purchase #5	$56.50	9.448%	$61.8381	$61.84	$61.85	$61.80
Purchase #6	$148.87	7.360%	$159.8268	$159.83	$159.85	$159.80
Purchase #7	$46.62	4.460%	$48.6993	$48.70	$48.70	$48.70
7 purchase totals =	$564.14		$615.4213	$615.43	$615.50	$615.30