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	$139.81	13.390%	$158.5306	$158.53	$158.55	$158.50
Purchase #2	$10.40	13.205%	$11.7733	$11.77	$11.75	$11.80
Purchase #3	$126.85	8.705%	$137.8923	$137.89	$137.90	$137.90
Purchase #4	$32.38	3.805%	$33.6121	$33.61	$33.60	$33.60
Purchase #5	$145.54	5.334%	$153.3031	$153.30	$153.30	$153.30
Purchase #6	$167.51	11.537%	$186.8356	$186.84	$186.85	$186.80
Purchase #7	$31.75	5.438%	$33.4766	$33.48	$33.50	$33.50
7 purchase totals =	$654.24		$715.4236	$715.42	$715.45	$715.40