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	$116.88	5.734%	$123.5819	$123.58	$123.60	$123.60
Purchase #2	$153.73	11.211%	$170.9647	$170.96	$170.95	$171.00
Purchase #3	$33.37	13.874%	$37.9998	$38.00	$38.00	$38.00
Purchase #4	$168.29	13.103%	$190.341	$190.34	$190.35	$190.30
Purchase #5	$164.27	12.144%	$184.2189	$184.22	$184.20	$184.20
Purchase #6	$94.59	9.261%	$103.35	$103.35	$103.35	$103.40
Purchase #7	$128.90	8.193%	$139.4608	$139.46	$139.45	$139.50
7 purchase totals =	$860.03		$949.9171	$949.91	$949.90	$950.00