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	$85.69	4.260%	$89.3404	$89.34	$89.35	$89.30
Purchase #2	$20.60	3.194%	$21.258	$21.26	$21.25	$21.30
Purchase #3	$185.72	7.419%	$199.4986	$199.50	$199.50	$199.50
Purchase #4	$11.61	3.167%	$11.9777	$11.98	$12.00	$12.00
Purchase #5	$70.64	12.450%	$79.4347	$79.43	$79.45	$79.40
Purchase #6	$133.72	9.807%	$146.8339	$146.83	$146.85	$146.80
Purchase #7	$23.95	3.296%	$24.7394	$24.74	$24.75	$24.70
7 purchase totals =	$531.93		$573.0827	$573.08	$573.15	$573.00