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	$114.91	11.683%	$128.3349	$128.33	$128.35	$128.30
Purchase #2	$152.60	5.740%	$161.3592	$161.36	$161.35	$161.40
Purchase #3	$80.25	13.266%	$90.896	$90.90	$90.90	$90.90
Purchase #4	$250.26	11.716%	$279.5805	$279.58	$279.60	$279.60
Purchase #5	$52.35	4.291%	$54.5963	$54.60	$54.60	$54.60
Purchase #6	$19.96	10.738%	$22.1033	$22.10	$22.10	$22.10
Purchase #7	$146.40	6.728%	$156.2498	$156.25	$156.25	$156.20
7 purchase totals =	$816.73		$893.1200	$893.12	$893.15	$893.10