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	$116.84	5.710%	$123.5116	$123.51	$123.50	$123.50
Purchase #2	$78.32	4.111%	$81.5397	$81.54	$81.55	$81.50
Purchase #3	$62.73	4.248%	$65.3948	$65.39	$65.40	$65.40
Purchase #4	$199.33	12.812%	$224.8682	$224.87	$224.85	$224.90
Purchase #5	$122.28	5.162%	$128.5921	$128.59	$128.60	$128.60
Purchase #6	$93.63	8.596%	$101.6784	$101.68	$101.70	$101.70
Purchase #7	$47.80	6.244%	$50.7846	$50.78	$50.80	$50.80
7 purchase totals =	$720.93		$776.3694	$776.36	$776.40	$776.40