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	$82.41	9.810%	$90.4944	$90.49	$90.50	$90.50
Purchase #2	$10.65	10.202%	$11.7365	$11.74	$11.75	$11.70
Purchase #3	$72.27	7.714%	$77.8449	$77.84	$77.85	$77.80
Purchase #4	$176.30	8.693%	$191.6258	$191.63	$191.65	$191.60
Purchase #5	$73.78	9.868%	$81.0606	$81.06	$81.05	$81.10
Purchase #6	$181.30	13.472%	$205.7247	$205.72	$205.70	$205.70
Purchase #7	$220.39	9.380%	$241.0626	$241.06	$241.05	$241.10
7 purchase totals =	$817.10		$899.5495	$899.54	$899.55	$899.50