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	$94.34	12.144%	$105.7966	$105.80	$105.80	$105.80
Purchase #2	$158.28	6.468%	$168.5176	$168.52	$168.50	$168.50
Purchase #3	$60.95	10.353%	$67.2602	$67.26	$67.25	$67.30
Purchase #4	$5.78	4.510%	$6.0407	$6.04	$6.05	$6.00
Purchase #5	$119.30	10.785%	$132.1665	$132.17	$132.15	$132.20
Purchase #6	$131.89	7.522%	$141.8108	$141.81	$141.80	$141.80
Purchase #7	$126.29	10.119%	$139.0693	$139.07	$139.05	$139.10
7 purchase totals =	$696.83		$760.6617	$760.67	$760.60	$760.70