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	$162.85	9.623%	$178.5211	$178.52	$178.50	$178.50
Purchase #2	$144.64	9.470%	$158.3374	$158.34	$158.35	$158.30
Purchase #3	$235.47	11.756%	$263.1519	$263.15	$263.15	$263.20
Purchase #4	$203.54	8.717%	$221.2826	$221.28	$221.30	$221.30
Purchase #5	$93.46	7.671%	$100.6293	$100.63	$100.65	$100.60
Purchase #6	$47.54	7.857%	$51.2752	$51.28	$51.30	$51.30
Purchase #7	$155.74	6.853%	$166.4129	$166.41	$166.40	$166.40
7 purchase totals =	$1,043.24		$1,139.6104	$1,139.61	$1,139.65	$1,139.60