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	$16.80	8.768%	$18.273	$18.27	$18.25	$18.30
Purchase #2	$39.54	7.733%	$42.5976	$42.60	$42.60	$42.60
Purchase #3	$228.73	9.692%	$250.8985	$250.90	$250.90	$250.90
Purchase #4	$217.39	10.852%	$240.9812	$240.98	$241.00	$241.00
Purchase #5	$104.94	6.118%	$111.3602	$111.36	$111.35	$111.40
Purchase #6	$41.76	4.572%	$43.6693	$43.67	$43.65	$43.70
Purchase #7	$25.44	7.423%	$27.3284	$27.33	$27.35	$27.30
7 purchase totals =	$674.60		$735.1082	$735.11	$735.10	$735.20