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	$19.86	3.625%	$20.5799	$20.58	$20.60	$20.60
Purchase #2	$173.69	10.198%	$191.4029	$191.40	$191.40	$191.40
Purchase #3	$78.62	9.253%	$85.8947	$85.89	$85.90	$85.90
Purchase #4	$178.87	4.699%	$187.2751	$187.28	$187.30	$187.30
Purchase #5	$126.44	10.188%	$139.3217	$139.32	$139.30	$139.30
Purchase #6	$152.59	8.789%	$166.0011	$166.00	$166.00	$166.00
Purchase #7	$97.27	10.542%	$107.5242	$107.52	$107.50	$107.50
7 purchase totals =	$827.34		$897.9996	$897.99	$898.00	$898.00