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	$19.30	13.567%	$21.9184	$21.92	$21.90	$21.90
Purchase #2	$30.42	6.109%	$32.2784	$32.28	$32.30	$32.30
Purchase #3	$244.29	13.628%	$277.5818	$277.58	$277.60	$277.60
Purchase #4	$200.94	10.674%	$222.3883	$222.39	$222.40	$222.40
Purchase #5	$92.54	9.850%	$101.6552	$101.66	$101.65	$101.70
Purchase #6	$164.68	4.229%	$171.6443	$171.64	$171.65	$171.60
Purchase #7	$67.91	10.273%	$74.8864	$74.89	$74.90	$74.90
7 purchase totals =	$820.08		$902.3528	$902.36	$902.40	$902.40