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	$14.77	7.570%	$15.8881	$15.89	$15.90	$15.90
Purchase #2	$219.31	4.653%	$229.5145	$229.51	$229.50	$229.50
Purchase #3	$205.81	13.820%	$234.2529	$234.25	$234.25	$234.30
Purchase #4	$51.91	8.423%	$56.2824	$56.28	$56.30	$56.30
Purchase #5	$85.88	5.396%	$90.5141	$90.51	$90.50	$90.50
Purchase #6	$160.27	3.116%	$165.264	$165.26	$165.25	$165.30
Purchase #7	$182.99	12.474%	$205.8162	$205.82	$205.80	$205.80
7 purchase totals =	$920.94		$997.5322	$997.52	$997.50	$997.60