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	$142.72	8.198%	$154.4202	$154.42	$154.40	$154.40
Purchase #2	$133.66	9.826%	$146.7934	$146.79	$146.80	$146.80
Purchase #3	$6.98	9.595%	$7.6497	$7.65	$7.65	$7.60
Purchase #4	$11.58	10.770%	$12.8272	$12.83	$12.85	$12.80
Purchase #5	$36.49	11.109%	$40.5437	$40.54	$40.55	$40.50
Purchase #6	$240.88	5.570%	$254.297	$254.30	$254.30	$254.30
Purchase #7	$174.75	9.262%	$190.9353	$190.94	$190.95	$190.90
7 purchase totals =	$747.06		$807.4665	$807.47	$807.50	$807.30