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	$86.48	4.828%	$90.6553	$90.66	$90.65	$90.70
Purchase #2	$137.70	9.710%	$151.0707	$151.07	$151.05	$151.10
Purchase #3	$250.47	8.350%	$271.3842	$271.38	$271.40	$271.40
Purchase #4	$54.73	5.219%	$57.5864	$57.59	$57.60	$57.60
Purchase #5	$58.59	12.513%	$65.9214	$65.92	$65.90	$65.90
Purchase #6	$136.36	11.103%	$151.5001	$151.50	$151.50	$151.50
Purchase #7	$28.52	13.126%	$32.2635	$32.26	$32.25	$32.30
7 purchase totals =	$752.85		$820.3816	$820.38	$820.35	$820.50