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	$144.96	11.354%	$161.4188	$161.42	$161.40	$161.40
Purchase #2	$99.31	5.794%	$105.064	$105.06	$105.05	$105.10
Purchase #3	$158.48	5.703%	$167.5181	$167.52	$167.50	$167.50
Purchase #4	$51.47	5.129%	$54.1099	$54.11	$54.10	$54.10
Purchase #5	$12.47	12.838%	$14.0709	$14.07	$14.05	$14.10
Purchase #6	$46.40	5.229%	$48.8263	$48.83	$48.85	$48.80
Purchase #7	$63.89	10.873%	$70.8368	$70.84	$70.85	$70.80
7 purchase totals =	$576.98		$621.8448	$621.85	$621.80	$621.80