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	$59.50	10.539%	$65.7707	$65.77	$65.75	$65.80
Purchase #2	$153.64	8.714%	$167.0282	$167.03	$167.05	$167.00
Purchase #3	$7.93	3.866%	$8.2366	$8.24	$8.25	$8.20
Purchase #4	$141.85	11.622%	$158.3358	$158.34	$158.35	$158.30
Purchase #5	$112.47	5.511%	$118.6682	$118.67	$118.65	$118.70
Purchase #6	$195.42	13.769%	$222.3274	$222.33	$222.35	$222.30
Purchase #7	$131.90	12.121%	$147.8876	$147.89	$147.90	$147.90
7 purchase totals =	$802.71		$888.2545	$888.27	$888.30	$888.20