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	$230.61	11.858%	$257.9557	$257.96	$257.95	$258.00
Purchase #2	$82.43	5.468%	$86.9373	$86.94	$86.95	$86.90
Purchase #3	$150.37	13.556%	$170.7542	$170.75	$170.75	$170.80
Purchase #4	$130.83	11.211%	$145.4974	$145.50	$145.50	$145.50
Purchase #5	$32.91	13.608%	$37.3884	$37.39	$37.40	$37.40
Purchase #6	$190.66	7.810%	$205.5505	$205.55	$205.55	$205.60
Purchase #7	$39.93	13.768%	$45.4276	$45.43	$45.45	$45.40
7 purchase totals =	$857.74		$949.5111	$949.52	$949.55	$949.60