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	$37.39	13.451%	$42.4193	$42.42	$42.40	$42.40
Purchase #2	$118.68	10.866%	$131.5758	$131.58	$131.60	$131.60
Purchase #3	$154.49	5.220%	$162.5544	$162.55	$162.55	$162.60
Purchase #4	$45.51	13.725%	$51.7562	$51.76	$51.75	$51.80
Purchase #5	$188.64	12.469%	$212.1615	$212.16	$212.15	$212.20
Purchase #6	$204.97	11.780%	$229.1155	$229.12	$229.10	$229.10
Purchase #7	$82.76	9.630%	$90.7298	$90.73	$90.75	$90.70
7 purchase totals =	$832.44		$920.3125	$920.32	$920.30	$920.40