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	$172.38	3.765%	$178.8701	$178.87	$178.85	$178.90
Purchase #2	$217.45	13.530%	$246.871	$246.87	$246.85	$246.90
Purchase #3	$97.45	9.185%	$106.4008	$106.40	$106.40	$106.40
Purchase #4	$194.89	5.299%	$205.2172	$205.22	$205.20	$205.20
Purchase #5	$198.27	9.833%	$217.7659	$217.77	$217.75	$217.80
Purchase #6	$135.90	3.143%	$140.1713	$140.17	$140.15	$140.20
Purchase #7	$115.41	10.404%	$127.4173	$127.42	$127.40	$127.40
7 purchase totals =	$1,131.75		$1,222.7136	$1,222.72	$1,222.60	$1,222.80