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	$121.94	4.388%	$127.2907	$127.29	$127.30	$127.30
Purchase #2	$250.52	3.340%	$258.8874	$258.89	$258.90	$258.90
Purchase #3	$48.29	13.307%	$54.716	$54.72	$54.70	$54.70
Purchase #4	$87.97	12.152%	$98.6601	$98.66	$98.65	$98.70
Purchase #5	$24.28	12.448%	$27.3024	$27.30	$27.30	$27.30
Purchase #6	$209.39	4.713%	$219.2586	$219.26	$219.25	$219.30
Purchase #7	$18.88	10.701%	$20.9003	$20.90	$20.90	$20.90
7 purchase totals =	$761.27		$807.0155	$807.02	$807.00	$807.10