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	$17.58	7.740%	$18.9407	$18.94	$18.95	$18.90
Purchase #2	$86.72	4.222%	$90.3813	$90.38	$90.40	$90.40
Purchase #3	$18.90	11.597%	$21.0918	$21.09	$21.10	$21.10
Purchase #4	$108.93	8.870%	$118.5921	$118.59	$118.60	$118.60
Purchase #5	$5.83	8.714%	$6.338	$6.34	$6.35	$6.30
Purchase #6	$133.28	4.290%	$138.9977	$139.00	$139.00	$139.00
Purchase #7	$106.82	6.672%	$113.947	$113.95	$113.95	$113.90
7 purchase totals =	$478.06		$508.2886	$508.29	$508.35	$508.20