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	$231.99	13.163%	$262.5268	$262.53	$262.55	$262.50
Purchase #2	$71.57	10.124%	$78.8157	$78.82	$78.80	$78.80
Purchase #3	$235.35	9.786%	$258.3814	$258.38	$258.40	$258.40
Purchase #4	$214.73	9.653%	$235.4579	$235.46	$235.45	$235.50
Purchase #5	$174.67	12.501%	$196.5055	$196.51	$196.50	$196.50
Purchase #6	$230.44	3.264%	$237.9616	$237.96	$237.95	$238.00
Purchase #7	$96.40	13.372%	$109.2906	$109.29	$109.30	$109.30
7 purchase totals =	$1,255.15		$1,378.9395	$1,378.95	$1,378.95	$1,379.00