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	$48.27	12.538%	$54.3221	$54.32	$54.30	$54.30
Purchase #2	$200.89	11.549%	$224.0908	$224.09	$224.10	$224.10
Purchase #3	$10.92	3.390%	$11.2902	$11.29	$11.30	$11.30
Purchase #4	$239.81	9.843%	$263.4145	$263.41	$263.40	$263.40
Purchase #5	$196.84	10.487%	$217.4826	$217.48	$217.50	$217.50
Purchase #6	$123.48	11.247%	$137.3678	$137.37	$137.35	$137.40
Purchase #7	$86.59	13.719%	$98.4693	$98.47	$98.45	$98.50
7 purchase totals =	$906.80		$1,006.4373	$1,006.43	$1,006.40	$1,006.50