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	$165.36	10.335%	$182.45	$182.45	$182.45	$182.50
Purchase #2	$85.33	5.511%	$90.0325	$90.03	$90.05	$90.00
Purchase #3	$68.97	12.326%	$77.4712	$77.47	$77.45	$77.50
Purchase #4	$62.70	4.850%	$65.741	$65.74	$65.75	$65.70
Purchase #5	$123.52	4.276%	$128.8017	$128.80	$128.80	$128.80
Purchase #6	$70.91	5.688%	$74.9434	$74.94	$74.95	$74.90
Purchase #7	$250.37	6.397%	$266.3862	$266.39	$266.40	$266.40
7 purchase totals =	$827.16		$885.8260	$885.82	$885.85	$885.80