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	$166.96	12.741%	$188.2324	$188.23	$188.25	$188.20
Purchase #2	$238.55	10.447%	$263.4713	$263.47	$263.45	$263.50
Purchase #3	$95.42	11.622%	$106.5097	$106.51	$106.50	$106.50
Purchase #4	$238.39	5.256%	$250.9198	$250.92	$250.90	$250.90
Purchase #5	$173.93	6.646%	$185.4894	$185.49	$185.50	$185.50
Purchase #6	$132.75	3.259%	$137.0763	$137.08	$137.10	$137.10
Purchase #7	$32.84	5.276%	$34.5726	$34.57	$34.55	$34.60
7 purchase totals =	$1,078.84		$1,166.2715	$1,166.27	$1,166.25	$1,166.30