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	$11.43	9.217%	$12.4835	$12.48	$12.50	$12.50
Purchase #2	$171.41	11.293%	$190.7673	$190.77	$190.75	$190.80
Purchase #3	$173.40	10.646%	$191.8602	$191.86	$191.85	$191.90
Purchase #4	$36.40	9.846%	$39.9839	$39.98	$40.00	$40.00
Purchase #5	$191.79	7.200%	$205.5989	$205.60	$205.60	$205.60
Purchase #6	$37.30	6.809%	$39.8398	$39.84	$39.85	$39.80
Purchase #7	$158.47	11.314%	$176.3993	$176.40	$176.40	$176.40
7 purchase totals =	$780.20		$856.9329	$856.93	$856.95	$857.00