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	$13.27	13.816%	$15.1034	$15.10	$15.10	$15.10
Purchase #2	$35.97	9.233%	$39.2911	$39.29	$39.30	$39.30
Purchase #3	$46.92	9.658%	$51.4515	$51.45	$51.45	$51.50
Purchase #4	$194.90	8.423%	$211.3164	$211.32	$211.30	$211.30
Purchase #5	$188.57	4.215%	$196.5182	$196.52	$196.50	$196.50
Purchase #6	$44.93	7.665%	$48.3739	$48.37	$48.35	$48.40
Purchase #7	$23.34	3.600%	$24.1802	$24.18	$24.20	$24.20
7 purchase totals =	$547.90		$586.2347	$586.23	$586.20	$586.30