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	$139.87	11.342%	$155.7341	$155.73	$155.75	$155.70
Purchase #2	$29.37	10.748%	$32.5267	$32.53	$32.55	$32.50
Purchase #3	$124.56	10.195%	$137.2589	$137.26	$137.25	$137.30
Purchase #4	$10.38	5.778%	$10.9798	$10.98	$11.00	$11.00
Purchase #5	$231.75	13.282%	$262.531	$262.53	$262.55	$262.50
Purchase #6	$139.90	8.752%	$152.144	$152.14	$152.15	$152.10
Purchase #7	$249.99	11.218%	$278.0339	$278.03	$278.05	$278.00
7 purchase totals =	$925.82		$1,029.2084	$1,029.20	$1,029.30	$1,029.10