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	$215.82	11.465%	$240.5638	$240.56	$240.55	$240.60
Purchase #2	$169.35	10.768%	$187.5856	$187.59	$187.60	$187.60
Purchase #3	$92.89	10.707%	$102.8357	$102.84	$102.85	$102.80
Purchase #4	$71.89	11.848%	$80.4075	$80.41	$80.40	$80.40
Purchase #5	$160.66	7.571%	$172.8236	$172.82	$172.80	$172.80
Purchase #6	$21.61	7.443%	$23.2184	$23.22	$23.20	$23.20
Purchase #7	$97.48	3.311%	$100.7076	$100.71	$100.70	$100.70
7 purchase totals =	$829.70		$908.1422	$908.15	$908.10	$908.10