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	$151.78	5.379%	$159.9442	$159.94	$159.95	$159.90
Purchase #2	$168.27	12.755%	$189.7328	$189.73	$189.75	$189.70
Purchase #3	$228.31	5.584%	$241.0588	$241.06	$241.05	$241.10
Purchase #4	$116.29	6.576%	$123.9372	$123.94	$123.95	$123.90
Purchase #5	$93.28	11.765%	$104.2544	$104.25	$104.25	$104.30
Purchase #6	$31.43	7.192%	$33.6904	$33.69	$33.70	$33.70
Purchase #7	$18.28	12.713%	$20.6039	$20.60	$20.60	$20.60
7 purchase totals =	$807.64		$873.2217	$873.21	$873.25	$873.20