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	$87.71	3.129%	$90.4544	$90.45	$90.45	$90.50
Purchase #2	$47.34	13.853%	$53.898	$53.90	$53.90	$53.90
Purchase #3	$156.48	5.419%	$164.9597	$164.96	$164.95	$165.00
Purchase #4	$18.70	13.864%	$21.2926	$21.29	$21.30	$21.30
Purchase #5	$59.75	7.821%	$64.423	$64.42	$64.40	$64.40
Purchase #6	$240.72	9.233%	$262.9457	$262.95	$262.95	$262.90
Purchase #7	$26.92	13.581%	$30.576	$30.58	$30.60	$30.60
7 purchase totals =	$637.62		$688.5494	$688.55	$688.55	$688.60