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	$31.78	7.522%	$34.1705	$34.17	$34.15	$34.20
Purchase #2	$149.42	12.615%	$168.2693	$168.27	$168.25	$168.30
Purchase #3	$214.31	12.604%	$241.3216	$241.32	$241.30	$241.30
Purchase #4	$108.32	13.496%	$122.9389	$122.94	$122.95	$122.90
Purchase #5	$202.34	9.557%	$221.6776	$221.68	$221.70	$221.70
Purchase #6	$219.32	5.557%	$231.5076	$231.51	$231.50	$231.50
Purchase #7	$79.40	13.707%	$90.2834	$90.28	$90.30	$90.30
7 purchase totals =	$1,004.89		$1,110.1689	$1,110.17	$1,110.15	$1,110.20