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	$80.88	10.428%	$89.3142	$89.31	$89.30	$89.30
Purchase #2	$41.43	12.387%	$46.5619	$46.56	$46.55	$46.60
Purchase #3	$157.51	13.185%	$178.2777	$178.28	$178.30	$178.30
Purchase #4	$60.86	4.172%	$63.3991	$63.40	$63.40	$63.40
Purchase #5	$137.70	6.455%	$146.5885	$146.59	$146.60	$146.60
Purchase #6	$155.70	6.669%	$166.0836	$166.08	$166.10	$166.10
Purchase #7	$229.34	6.854%	$245.059	$245.06	$245.05	$245.10
7 purchase totals =	$863.42		$935.2840	$935.28	$935.30	$935.40