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	$93.83	5.766%	$99.2402	$99.24	$99.25	$99.20
Purchase #2	$31.49	13.835%	$35.8466	$35.85	$35.85	$35.80
Purchase #3	$77.38	5.663%	$81.762	$81.76	$81.75	$81.80
Purchase #4	$215.45	3.576%	$223.1545	$223.15	$223.15	$223.20
Purchase #5	$48.75	8.492%	$52.8899	$52.89	$52.90	$52.90
Purchase #6	$172.91	10.332%	$190.7751	$190.78	$190.80	$190.80
Purchase #7	$84.58	6.694%	$90.2418	$90.24	$90.25	$90.20
7 purchase totals =	$724.39		$773.9101	$773.91	$773.95	$773.90