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	$123.93	12.281%	$139.1498	$139.15	$139.15	$139.10
Purchase #2	$80.82	11.324%	$89.9721	$89.97	$89.95	$90.00
Purchase #3	$94.53	4.368%	$98.6591	$98.66	$98.65	$98.70
Purchase #4	$18.32	13.242%	$20.7459	$20.75	$20.75	$20.70
Purchase #5	$118.31	10.335%	$130.5373	$130.54	$130.55	$130.50
Purchase #6	$50.27	3.147%	$51.852	$51.85	$51.85	$51.90
Purchase #7	$132.27	11.521%	$147.5088	$147.51	$147.50	$147.50
7 purchase totals =	$618.45		$678.4250	$678.43	$678.40	$678.40