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	$230.86	9.725%	$253.3111	$253.31	$253.30	$253.30
Purchase #2	$250.70	11.333%	$279.1118	$279.11	$279.10	$279.10
Purchase #3	$110.34	10.575%	$122.0085	$122.01	$122.00	$122.00
Purchase #4	$54.65	8.142%	$59.0996	$59.10	$59.10	$59.10
Purchase #5	$215.87	10.681%	$238.9271	$238.93	$238.95	$238.90
Purchase #6	$20.78	3.462%	$21.4994	$21.50	$21.50	$21.50
Purchase #7	$197.70	7.537%	$212.6006	$212.60	$212.60	$212.60
7 purchase totals =	$1,080.90		$1,186.5581	$1,186.56	$1,186.55	$1,186.50