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	$151.39	5.662%	$159.9617	$159.96	$159.95	$160.00
Purchase #2	$182.86	4.726%	$191.502	$191.50	$191.50	$191.50
Purchase #3	$11.39	10.476%	$12.5832	$12.58	$12.60	$12.60
Purchase #4	$82.77	9.661%	$90.7664	$90.77	$90.75	$90.80
Purchase #5	$25.89	4.647%	$27.0931	$27.09	$27.10	$27.10
Purchase #6	$181.45	12.472%	$204.0804	$204.08	$204.10	$204.10
Purchase #7	$150.38	9.414%	$164.5368	$164.54	$164.55	$164.50
7 purchase totals =	$786.13		$850.5236	$850.52	$850.55	$850.60