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	$153.50	12.288%	$172.3621	$172.36	$172.35	$172.40
Purchase #2	$74.70	9.480%	$81.7816	$81.78	$81.80	$81.80
Purchase #3	$142.33	7.225%	$152.6133	$152.61	$152.60	$152.60
Purchase #4	$80.66	12.294%	$90.5763	$90.58	$90.60	$90.60
Purchase #5	$125.67	10.597%	$138.9872	$138.99	$139.00	$139.00
Purchase #6	$233.95	11.810%	$261.5795	$261.58	$261.60	$261.60
Purchase #7	$99.36	5.454%	$104.7791	$104.78	$104.80	$104.80
7 purchase totals =	$910.17		$1,002.6791	$1,002.68	$1,002.75	$1,002.80