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	$24.54	11.866%	$27.4519	$27.45	$27.45	$27.50
Purchase #2	$201.67	11.155%	$224.1663	$224.17	$224.15	$224.20
Purchase #3	$99.90	8.514%	$108.4055	$108.41	$108.40	$108.40
Purchase #4	$57.38	9.662%	$62.9241	$62.92	$62.90	$62.90
Purchase #5	$91.56	8.480%	$99.3243	$99.32	$99.30	$99.30
Purchase #6	$56.95	4.778%	$59.6711	$59.67	$59.65	$59.70
Purchase #7	$111.27	3.183%	$114.8117	$114.81	$114.80	$114.80
7 purchase totals =	$643.27		$696.7549	$696.75	$696.65	$696.80