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	$54.41	11.117%	$60.4588	$60.46	$60.45	$60.50
Purchase #2	$91.83	9.673%	$100.7127	$100.71	$100.70	$100.70
Purchase #3	$153.55	6.843%	$164.0574	$164.06	$164.05	$164.10
Purchase #4	$122.68	7.144%	$131.4443	$131.44	$131.45	$131.40
Purchase #5	$29.70	7.245%	$31.8518	$31.85	$31.85	$31.90
Purchase #6	$210.78	8.450%	$228.5909	$228.59	$228.60	$228.60
Purchase #7	$230.63	9.739%	$253.0911	$253.09	$253.10	$253.10
7 purchase totals =	$893.58		$970.2070	$970.20	$970.20	$970.30