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	$84.35	12.314%	$94.7369	$94.74	$94.75	$94.70
Purchase #2	$80.39	4.366%	$83.8998	$83.90	$83.90	$83.90
Purchase #3	$227.78	5.626%	$240.5949	$240.59	$240.60	$240.60
Purchase #4	$66.36	6.237%	$70.4989	$70.50	$70.50	$70.50
Purchase #5	$230.41	4.211%	$240.1126	$240.11	$240.10	$240.10
Purchase #6	$101.56	13.749%	$115.5235	$115.52	$115.50	$115.50
Purchase #7	$117.25	13.124%	$132.6379	$132.64	$132.65	$132.60
7 purchase totals =	$908.10		$978.0045	$978.00	$978.00	$977.90