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	$161.71	5.330%	$170.3291	$170.33	$170.35	$170.30
Purchase #2	$158.50	13.508%	$179.9102	$179.91	$179.90	$179.90
Purchase #3	$167.59	3.159%	$172.8842	$172.88	$172.90	$172.90
Purchase #4	$100.35	6.624%	$106.9972	$107.00	$107.00	$107.00
Purchase #5	$246.64	10.233%	$271.8787	$271.88	$271.90	$271.90
Purchase #6	$142.58	7.416%	$153.1537	$153.15	$153.15	$153.20
Purchase #7	$21.85	10.511%	$24.1467	$24.15	$24.15	$24.10
7 purchase totals =	$999.22		$1,079.2998	$1,079.30	$1,079.35	$1,079.30