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	$172.44	3.399%	$178.3012	$178.30	$178.30	$178.30
Purchase #2	$132.89	5.520%	$140.2255	$140.23	$140.25	$140.20
Purchase #3	$240.45	7.540%	$258.5799	$258.58	$258.60	$258.60
Purchase #4	$237.94	10.394%	$262.6715	$262.67	$262.65	$262.70
Purchase #5	$127.89	5.505%	$134.9303	$134.93	$134.95	$134.90
Purchase #6	$233.61	7.698%	$251.5933	$251.59	$251.60	$251.60
Purchase #7	$147.32	10.250%	$162.4203	$162.42	$162.40	$162.40
7 purchase totals =	$1,292.54		$1,388.7220	$1,388.72	$1,388.75	$1,388.70