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	$82.85	7.789%	$89.3032	$89.30	$89.30	$89.30
Purchase #2	$210.61	7.255%	$225.8898	$225.89	$225.90	$225.90
Purchase #3	$192.52	6.593%	$205.2128	$205.21	$205.20	$205.20
Purchase #4	$111.94	7.390%	$120.2124	$120.21	$120.20	$120.20
Purchase #5	$42.58	6.838%	$45.4916	$45.49	$45.50	$45.50
Purchase #6	$143.37	10.131%	$157.8948	$157.89	$157.90	$157.90
Purchase #7	$93.90	6.151%	$99.6758	$99.68	$99.70	$99.70
7 purchase totals =	$877.77		$943.6804	$943.67	$943.70	$943.70