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	$77.40	10.710%	$85.6895	$85.69	$85.70	$85.70
Purchase #2	$55.47	9.510%	$60.7452	$60.75	$60.75	$60.70
Purchase #3	$250.63	13.616%	$284.7558	$284.76	$284.75	$284.80
Purchase #4	$55.49	10.743%	$61.4513	$61.45	$61.45	$61.50
Purchase #5	$153.35	3.236%	$158.3124	$158.31	$158.30	$158.30
Purchase #6	$130.97	4.782%	$137.233	$137.23	$137.25	$137.20
Purchase #7	$74.99	10.548%	$82.8999	$82.90	$82.90	$82.90
7 purchase totals =	$798.30		$871.0871	$871.09	$871.10	$871.10