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	$14.72	3.537%	$15.2406	$15.24	$15.25	$15.20
Purchase #2	$120.78	11.541%	$134.7192	$134.72	$134.70	$134.70
Purchase #3	$86.81	13.332%	$98.3835	$98.38	$98.40	$98.40
Purchase #4	$32.32	4.218%	$33.6833	$33.68	$33.70	$33.70
Purchase #5	$142.42	5.832%	$150.7259	$150.73	$150.75	$150.70
Purchase #6	$227.47	8.745%	$247.3623	$247.36	$247.35	$247.40
Purchase #7	$90.33	10.144%	$99.4931	$99.49	$99.50	$99.50
7 purchase totals =	$714.85		$779.6079	$779.60	$779.65	$779.60