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	$249.86	8.706%	$271.6128	$271.61	$271.60	$271.60
Purchase #2	$103.43	6.621%	$110.2781	$110.28	$110.30	$110.30
Purchase #3	$86.96	10.187%	$95.8186	$95.82	$95.80	$95.80
Purchase #4	$227.68	12.592%	$256.3495	$256.35	$256.35	$256.30
Purchase #5	$113.79	12.798%	$128.3528	$128.35	$128.35	$128.40
Purchase #6	$59.72	4.463%	$62.3853	$62.39	$62.40	$62.40
Purchase #7	$209.83	9.706%	$230.1961	$230.20	$230.20	$230.20
7 purchase totals =	$1,051.27		$1,154.9932	$1,155.00	$1,155.00	$1,155.00