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	$185.59	3.744%	$192.5385	$192.54	$192.55	$192.50
Purchase #2	$80.83	11.377%	$90.026	$90.03	$90.05	$90.00
Purchase #3	$17.88	11.848%	$19.9984	$20.00	$20.00	$20.00
Purchase #4	$51.58	6.415%	$54.8889	$54.89	$54.90	$54.90
Purchase #5	$80.62	10.323%	$88.9424	$88.94	$88.95	$88.90
Purchase #6	$136.83	5.448%	$144.2845	$144.28	$144.30	$144.30
Purchase #7	$244.27	11.541%	$272.4612	$272.46	$272.45	$272.50
7 purchase totals =	$797.60		$863.1399	$863.14	$863.20	$863.10