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	$110.83	6.716%	$118.2733	$118.27	$118.25	$118.30
Purchase #2	$120.94	6.212%	$128.4528	$128.45	$128.45	$128.50
Purchase #3	$99.80	11.641%	$111.4177	$111.42	$111.40	$111.40
Purchase #4	$173.32	9.110%	$189.1095	$189.11	$189.10	$189.10
Purchase #5	$149.72	5.235%	$157.5578	$157.56	$157.55	$157.60
Purchase #6	$144.94	5.176%	$152.4421	$152.44	$152.45	$152.40
Purchase #7	$94.49	10.721%	$104.6203	$104.62	$104.60	$104.60
7 purchase totals =	$894.04		$961.8735	$961.87	$961.80	$961.90