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	$121.52	13.614%	$138.0637	$138.06	$138.05	$138.10
Purchase #2	$103.48	13.531%	$117.4819	$117.48	$117.50	$117.50
Purchase #3	$54.98	9.866%	$60.4043	$60.40	$60.40	$60.40
Purchase #4	$40.52	6.730%	$43.247	$43.25	$43.25	$43.20
Purchase #5	$173.75	3.252%	$179.4004	$179.40	$179.40	$179.40
Purchase #6	$132.74	8.765%	$144.3747	$144.37	$144.35	$144.40
Purchase #7	$99.98	9.495%	$109.4731	$109.47	$109.45	$109.50
7 purchase totals =	$726.97		$792.4451	$792.43	$792.40	$792.50