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	$53.93	11.768%	$60.2765	$60.28	$60.30	$60.30
Purchase #2	$186.49	5.414%	$196.5866	$196.59	$196.60	$196.60
Purchase #3	$55.51	6.301%	$59.0077	$59.01	$59.00	$59.00
Purchase #4	$124.43	13.392%	$141.0937	$141.09	$141.10	$141.10
Purchase #5	$39.89	5.479%	$42.0756	$42.08	$42.10	$42.10
Purchase #6	$70.43	12.239%	$79.0499	$79.05	$79.05	$79.00
Purchase #7	$12.85	9.505%	$14.0714	$14.07	$14.05	$14.10
7 purchase totals =	$543.53		$592.1614	$592.17	$592.20	$592.20