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	$32.68	11.616%	$36.4761	$36.48	$36.50	$36.50
Purchase #2	$20.42	6.641%	$21.7761	$21.78	$21.80	$21.80
Purchase #3	$10.84	10.452%	$11.973	$11.97	$11.95	$12.00
Purchase #4	$220.64	13.501%	$250.4286	$250.43	$250.45	$250.40
Purchase #5	$108.82	5.762%	$115.0902	$115.09	$115.10	$115.10
Purchase #6	$215.47	6.530%	$229.5402	$229.54	$229.55	$229.50
Purchase #7	$103.57	7.271%	$111.1006	$111.10	$111.10	$111.10
7 purchase totals =	$712.44		$776.3848	$776.39	$776.45	$776.40