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	$76.81	6.867%	$82.0845	$82.08	$82.10	$82.10
Purchase #2	$11.73	3.325%	$12.12	$12.12	$12.10	$12.10
Purchase #3	$145.87	12.740%	$164.4538	$164.45	$164.45	$164.50
Purchase #4	$162.28	10.458%	$179.2512	$179.25	$179.25	$179.30
Purchase #5	$134.53	7.430%	$144.5256	$144.53	$144.55	$144.50
Purchase #6	$44.72	11.317%	$49.781	$49.78	$49.80	$49.80
Purchase #7	$6.59	13.701%	$7.4929	$7.49	$7.50	$7.50
7 purchase totals =	$582.53		$639.7090	$639.70	$639.75	$639.80