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	$38.89	9.241%	$42.4838	$42.48	$42.50	$42.50
Purchase #2	$173.80	11.671%	$194.0842	$194.08	$194.10	$194.10
Purchase #3	$70.37	12.231%	$78.977	$78.98	$79.00	$79.00
Purchase #4	$28.99	4.785%	$30.3772	$30.38	$30.40	$30.40
Purchase #5	$184.87	6.499%	$196.8847	$196.88	$196.90	$196.90
Purchase #6	$84.72	12.462%	$95.2778	$95.28	$95.30	$95.30
Purchase #7	$160.52	10.224%	$176.9316	$176.93	$176.95	$176.90
7 purchase totals =	$742.16		$815.0163	$815.01	$815.15	$815.10