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	$135.75	7.617%	$146.0901	$146.09	$146.10	$146.10
Purchase #2	$158.91	3.808%	$164.9613	$164.96	$164.95	$165.00
Purchase #3	$32.65	4.582%	$34.146	$34.15	$34.15	$34.10
Purchase #4	$92.68	8.250%	$100.3261	$100.33	$100.35	$100.30
Purchase #5	$165.88	4.349%	$173.0941	$173.09	$173.10	$173.10
Purchase #6	$25.60	7.454%	$27.5082	$27.51	$27.50	$27.50
Purchase #7	$27.98	13.466%	$31.7478	$31.75	$31.75	$31.70
7 purchase totals =	$639.45		$677.8736	$677.88	$677.90	$677.80