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	$40.42	7.144%	$43.3076	$43.31	$43.30	$43.30
Purchase #2	$156.61	10.568%	$173.1605	$173.16	$173.15	$173.20
Purchase #3	$109.45	8.778%	$119.0575	$119.06	$119.05	$119.10
Purchase #4	$65.51	13.587%	$74.4108	$74.41	$74.40	$74.40
Purchase #5	$201.94	9.362%	$220.8456	$220.85	$220.85	$220.80
Purchase #6	$13.60	10.732%	$15.0596	$15.06	$15.05	$15.10
Purchase #7	$181.78	10.320%	$200.5397	$200.54	$200.55	$200.50
7 purchase totals =	$769.31		$846.3813	$846.39	$846.35	$846.40