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	$240.55	6.222%	$255.517	$255.52	$255.50	$255.50
Purchase #2	$147.74	3.238%	$152.5238	$152.52	$152.50	$152.50
Purchase #3	$38.93	7.692%	$41.9245	$41.92	$41.90	$41.90
Purchase #4	$132.96	9.470%	$145.5513	$145.55	$145.55	$145.60
Purchase #5	$143.67	4.343%	$149.9096	$149.91	$149.90	$149.90
Purchase #6	$109.91	4.128%	$114.4471	$114.45	$114.45	$114.40
Purchase #7	$17.85	6.301%	$18.9747	$18.97	$18.95	$19.00
7 purchase totals =	$831.61		$878.8480	$878.84	$878.75	$878.80