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	$228.71	9.826%	$251.183	$251.18	$251.20	$251.20
Purchase #2	$57.31	7.286%	$61.4856	$61.49	$61.50	$61.50
Purchase #3	$168.47	11.454%	$187.7666	$187.77	$187.75	$187.80
Purchase #4	$37.94	9.654%	$41.6027	$41.60	$41.60	$41.60
Purchase #5	$128.69	4.400%	$134.3524	$134.35	$134.35	$134.40
Purchase #6	$142.28	4.572%	$148.785	$148.79	$148.80	$148.80
Purchase #7	$156.32	11.682%	$174.5813	$174.58	$174.60	$174.60
7 purchase totals =	$919.72		$999.7566	$999.76	$999.80	$999.90