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	$22.44	7.570%	$24.1387	$24.14	$24.15	$24.10
Purchase #2	$38.72	11.318%	$43.1023	$43.10	$43.10	$43.10
Purchase #3	$31.25	10.474%	$34.5231	$34.52	$34.50	$34.50
Purchase #4	$230.70	4.702%	$241.5475	$241.55	$241.55	$241.50
Purchase #5	$72.84	5.495%	$76.8426	$76.84	$76.85	$76.80
Purchase #6	$167.88	12.291%	$188.5141	$188.51	$188.50	$188.50
Purchase #7	$57.59	8.691%	$62.5951	$62.60	$62.60	$62.60
7 purchase totals =	$621.42		$671.2634	$671.26	$671.25	$671.10