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	$183.52	3.643%	$190.2056	$190.21	$190.20	$190.20
Purchase #2	$172.80	8.527%	$187.5347	$187.53	$187.55	$187.50
Purchase #3	$240.91	8.716%	$261.9077	$261.91	$261.90	$261.90
Purchase #4	$137.44	5.168%	$144.5429	$144.54	$144.55	$144.50
Purchase #5	$127.79	10.761%	$141.5415	$141.54	$141.55	$141.50
Purchase #6	$172.60	13.268%	$195.5006	$195.50	$195.50	$195.50
Purchase #7	$80.55	11.748%	$90.013	$90.01	$90.00	$90.00
7 purchase totals =	$1,115.61		$1,211.2460	$1,211.24	$1,211.25	$1,211.10