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	$27.96	12.501%	$31.4553	$31.46	$31.45	$31.50
Purchase #2	$218.61	5.675%	$231.0161	$231.02	$231.00	$231.00
Purchase #3	$137.85	12.194%	$154.6594	$154.66	$154.65	$154.70
Purchase #4	$173.50	12.193%	$194.6549	$194.65	$194.65	$194.70
Purchase #5	$112.73	9.452%	$123.3852	$123.39	$123.40	$123.40
Purchase #6	$187.96	4.466%	$196.3543	$196.35	$196.35	$196.40
Purchase #7	$169.86	10.520%	$187.7293	$187.73	$187.75	$187.70
7 purchase totals =	$1,028.47		$1,119.2545	$1,119.26	$1,119.25	$1,119.40