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	$24.42	8.353%	$26.4598	$26.46	$26.45	$26.50
Purchase #2	$143.71	4.772%	$150.5678	$150.57	$150.55	$150.60
Purchase #3	$27.39	7.117%	$29.3393	$29.34	$29.35	$29.30
Purchase #4	$152.68	13.367%	$173.0887	$173.09	$173.10	$173.10
Purchase #5	$72.43	11.296%	$80.6117	$80.61	$80.60	$80.60
Purchase #6	$183.89	3.829%	$190.9311	$190.93	$190.95	$190.90
Purchase #7	$239.65	3.700%	$248.5171	$248.52	$248.50	$248.50
7 purchase totals =	$844.17		$899.5155	$899.52	$899.50	$899.50