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	$108.64	13.515%	$123.3227	$123.32	$123.30	$123.30
Purchase #2	$134.58	4.428%	$140.5392	$140.54	$140.55	$140.50
Purchase #3	$236.52	7.185%	$253.514	$253.51	$253.50	$253.50
Purchase #4	$65.41	9.530%	$71.6436	$71.64	$71.65	$71.60
Purchase #5	$71.65	7.778%	$77.2229	$77.22	$77.20	$77.20
Purchase #6	$138.96	3.326%	$143.5818	$143.58	$143.60	$143.60
Purchase #7	$149.32	4.787%	$156.4679	$156.47	$156.45	$156.50
7 purchase totals =	$905.08		$966.2921	$966.28	$966.25	$966.20