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	$242.78	6.515%	$258.5971	$258.60	$258.60	$258.60
Purchase #2	$181.91	3.284%	$187.8839	$187.88	$187.90	$187.90
Purchase #3	$191.35	7.490%	$205.6821	$205.68	$205.70	$205.70
Purchase #4	$220.53	3.357%	$227.9332	$227.93	$227.95	$227.90
Purchase #5	$68.90	5.230%	$72.5035	$72.50	$72.50	$72.50
Purchase #6	$29.94	10.585%	$33.1091	$33.11	$33.10	$33.10
Purchase #7	$57.87	7.833%	$62.403	$62.40	$62.40	$62.40
7 purchase totals =	$993.28		$1,048.1119	$1,048.10	$1,048.15	$1,048.10