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	$30.52	4.759%	$31.9724	$31.97	$31.95	$32.00
Purchase #2	$105.76	6.570%	$112.7084	$112.71	$112.70	$112.70
Purchase #3	$209.88	4.267%	$218.8356	$218.84	$218.85	$218.80
Purchase #4	$101.45	9.700%	$111.2907	$111.29	$111.30	$111.30
Purchase #5	$239.76	12.745%	$270.3174	$270.32	$270.30	$270.30
Purchase #6	$241.86	4.431%	$252.5768	$252.58	$252.60	$252.60
Purchase #7	$95.49	5.110%	$100.3695	$100.37	$100.35	$100.40
7 purchase totals =	$1,024.72		$1,098.0708	$1,098.08	$1,098.05	$1,098.10