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	$86.40	9.249%	$94.3911	$94.39	$94.40	$94.40
Purchase #2	$54.55	3.662%	$56.5476	$56.55	$56.55	$56.50
Purchase #3	$99.95	6.554%	$106.5007	$106.50	$106.50	$106.50
Purchase #4	$183.51	13.536%	$208.3499	$208.35	$208.35	$208.30
Purchase #5	$33.64	12.224%	$37.7522	$37.75	$37.75	$37.80
Purchase #6	$132.95	8.347%	$144.0473	$144.05	$144.05	$144.00
Purchase #7	$196.95	13.288%	$223.1207	$223.12	$223.10	$223.10
7 purchase totals =	$787.95		$870.7095	$870.71	$870.70	$870.60