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	$131.74	9.434%	$144.1684	$144.17	$144.15	$144.20
Purchase #2	$123.44	13.734%	$140.3932	$140.39	$140.40	$140.40
Purchase #3	$106.33	9.205%	$116.1177	$116.12	$116.10	$116.10
Purchase #4	$65.37	10.766%	$72.4077	$72.41	$72.40	$72.40
Purchase #5	$246.36	13.410%	$279.3969	$279.40	$279.40	$279.40
Purchase #6	$104.62	7.184%	$112.1359	$112.14	$112.15	$112.10
Purchase #7	$193.90	5.658%	$204.8709	$204.87	$204.85	$204.90
7 purchase totals =	$971.76		$1,069.4907	$1,069.50	$1,069.45	$1,069.50