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	$120.54	10.217%	$132.8556	$132.86	$132.85	$132.90
Purchase #2	$64.46	5.533%	$68.0266	$68.03	$68.05	$68.00
Purchase #3	$47.69	7.795%	$51.4074	$51.41	$51.40	$51.40
Purchase #4	$139.64	13.587%	$158.6129	$158.61	$158.60	$158.60
Purchase #5	$67.34	8.196%	$72.8592	$72.86	$72.85	$72.90
Purchase #6	$136.52	12.103%	$153.043	$153.04	$153.05	$153.00
Purchase #7	$64.71	9.371%	$70.774	$70.77	$70.75	$70.80
7 purchase totals =	$640.90		$707.5787	$707.58	$707.55	$707.60