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	$249.46	13.246%	$282.5035	$282.50	$282.50	$282.50
Purchase #2	$113.36	13.393%	$128.5423	$128.54	$128.55	$128.50
Purchase #3	$174.32	7.678%	$187.7043	$187.70	$187.70	$187.70
Purchase #4	$219.39	4.550%	$229.3722	$229.37	$229.35	$229.40
Purchase #5	$197.60	13.798%	$224.8648	$224.86	$224.85	$224.90
Purchase #6	$181.30	8.326%	$196.395	$196.40	$196.40	$196.40
Purchase #7	$49.84	7.124%	$53.3906	$53.39	$53.40	$53.40
7 purchase totals =	$1,185.27		$1,302.7727	$1,302.76	$1,302.75	$1,302.80