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	$91.51	4.115%	$95.2756	$95.28	$95.30	$95.30
Purchase #2	$51.30	8.537%	$55.6795	$55.68	$55.70	$55.70
Purchase #3	$142.67	5.136%	$149.9975	$150.00	$150.00	$150.00
Purchase #4	$123.34	13.161%	$139.5728	$139.57	$139.55	$139.60
Purchase #5	$169.35	9.157%	$184.8574	$184.86	$184.85	$184.90
Purchase #6	$59.70	11.451%	$66.5362	$66.54	$66.55	$66.50
Purchase #7	$104.37	4.840%	$109.4215	$109.42	$109.40	$109.40
7 purchase totals =	$742.24		$801.3405	$801.35	$801.35	$801.40