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	$103.27	10.290%	$113.8965	$113.90	$113.90	$113.90
Purchase #2	$55.47	8.126%	$59.9775	$59.98	$60.00	$60.00
Purchase #3	$65.92	6.348%	$70.1046	$70.10	$70.10	$70.10
Purchase #4	$29.26	10.223%	$32.2512	$32.25	$32.25	$32.30
Purchase #5	$120.76	5.770%	$127.7279	$127.73	$127.75	$127.70
Purchase #6	$158.93	11.762%	$177.6233	$177.62	$177.60	$177.60
Purchase #7	$15.95	13.136%	$18.0452	$18.05	$18.05	$18.00
7 purchase totals =	$549.56		$599.6262	$599.63	$599.65	$599.60