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	$98.83	3.778%	$102.5638	$102.56	$102.55	$102.60
Purchase #2	$104.84	3.489%	$108.4979	$108.50	$108.50	$108.50
Purchase #3	$60.28	6.695%	$64.3157	$64.32	$64.30	$64.30
Purchase #4	$215.92	8.786%	$234.8907	$234.89	$234.90	$234.90
Purchase #5	$19.65	9.851%	$21.5857	$21.59	$21.60	$21.60
Purchase #6	$38.75	10.152%	$42.6839	$42.68	$42.70	$42.70
Purchase #7	$129.89	9.621%	$142.3867	$142.39	$142.40	$142.40
7 purchase totals =	$668.16		$716.9244	$716.93	$716.95	$717.00