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	$86.74	4.250%	$90.4265	$90.43	$90.45	$90.40
Purchase #2	$176.30	8.773%	$191.7668	$191.77	$191.75	$191.80
Purchase #3	$212.41	10.148%	$233.9654	$233.97	$233.95	$234.00
Purchase #4	$111.72	12.786%	$126.0045	$126.00	$126.00	$126.00
Purchase #5	$144.44	11.852%	$161.559	$161.56	$161.55	$161.60
Purchase #6	$109.83	6.348%	$116.802	$116.80	$116.80	$116.80
Purchase #7	$28.57	12.358%	$32.1007	$32.10	$32.10	$32.10
7 purchase totals =	$870.01		$952.6249	$952.63	$952.60	$952.70