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	$25.47	13.565%	$28.925	$28.93	$28.95	$28.90
Purchase #2	$229.84	12.545%	$258.6734	$258.67	$258.65	$258.70
Purchase #3	$226.44	9.304%	$247.508	$247.51	$247.50	$247.50
Purchase #4	$155.30	10.603%	$171.7665	$171.77	$171.75	$171.80
Purchase #5	$243.44	12.712%	$274.3861	$274.39	$274.40	$274.40
Purchase #6	$187.72	4.602%	$196.3589	$196.36	$196.35	$196.40
Purchase #7	$77.86	9.509%	$85.2637	$85.26	$85.25	$85.30
7 purchase totals =	$1,146.07		$1,262.8816	$1,262.89	$1,262.85	$1,263.00