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	$137.68	10.622%	$152.3044	$152.30	$152.30	$152.30
Purchase #2	$211.72	6.824%	$226.1678	$226.17	$226.15	$226.20
Purchase #3	$98.77	10.144%	$108.7892	$108.79	$108.80	$108.80
Purchase #4	$237.89	11.176%	$264.4766	$264.48	$264.50	$264.50
Purchase #5	$241.92	9.384%	$264.6218	$264.62	$264.60	$264.60
Purchase #6	$117.39	4.271%	$122.4037	$122.40	$122.40	$122.40
Purchase #7	$182.78	9.874%	$200.8277	$200.83	$200.85	$200.80
7 purchase totals =	$1,228.15		$1,339.5912	$1,339.59	$1,339.60	$1,339.60