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	$224.99	13.423%	$255.1904	$255.19	$255.20	$255.20
Purchase #2	$164.92	3.418%	$170.557	$170.56	$170.55	$170.60
Purchase #3	$89.83	11.688%	$100.3293	$100.33	$100.35	$100.30
Purchase #4	$196.92	3.151%	$203.1249	$203.12	$203.10	$203.10
Purchase #5	$25.64	11.454%	$28.5768	$28.58	$28.60	$28.60
Purchase #6	$180.50	3.848%	$187.4456	$187.45	$187.45	$187.40
Purchase #7	$139.76	10.649%	$154.643	$154.64	$154.65	$154.60
7 purchase totals =	$1,022.56		$1,099.8670	$1,099.87	$1,099.90	$1,099.80