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	$38.67	9.170%	$42.216	$42.22	$42.20	$42.20
Purchase #2	$214.64	13.148%	$242.8609	$242.86	$242.85	$242.90
Purchase #3	$21.53	13.102%	$24.3509	$24.35	$24.35	$24.40
Purchase #4	$166.31	9.192%	$181.5972	$181.60	$181.60	$181.60
Purchase #5	$209.45	6.209%	$222.4548	$222.45	$222.45	$222.50
Purchase #6	$18.86	10.495%	$20.8394	$20.84	$20.85	$20.80
Purchase #7	$119.28	10.604%	$131.9285	$131.93	$131.95	$131.90
7 purchase totals =	$788.74		$866.2477	$866.25	$866.25	$866.30