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	$70.57	13.349%	$79.9904	$79.99	$80.00	$80.00
Purchase #2	$112.37	13.316%	$127.3332	$127.33	$127.35	$127.30
Purchase #3	$155.73	10.429%	$171.9711	$171.97	$171.95	$172.00
Purchase #4	$243.72	5.593%	$257.3513	$257.35	$257.35	$257.40
Purchase #5	$81.39	3.141%	$83.9465	$83.95	$83.95	$83.90
Purchase #6	$168.52	13.197%	$190.7596	$190.76	$190.75	$190.80
Purchase #7	$121.97	4.516%	$127.4782	$127.48	$127.50	$127.50
7 purchase totals =	$954.27		$1,038.8303	$1,038.83	$1,038.85	$1,038.90