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	$187.89	13.331%	$212.9376	$212.94	$212.95	$212.90
Purchase #2	$86.82	8.413%	$94.1242	$94.12	$94.10	$94.10
Purchase #3	$105.84	11.353%	$117.856	$117.86	$117.85	$117.90
Purchase #4	$72.99	11.828%	$81.6233	$81.62	$81.60	$81.60
Purchase #5	$64.86	11.495%	$72.3157	$72.32	$72.30	$72.30
Purchase #6	$234.38	6.447%	$249.4905	$249.49	$249.50	$249.50
Purchase #7	$101.81	9.787%	$111.7741	$111.77	$111.75	$111.80
7 purchase totals =	$854.59		$940.1214	$940.12	$940.05	$940.10