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	$57.60	8.510%	$62.5018	$62.50	$62.50	$62.50
Purchase #2	$173.56	6.845%	$185.4402	$185.44	$185.45	$185.40
Purchase #3	$114.33	12.374%	$128.4772	$128.48	$128.50	$128.50
Purchase #4	$196.40	13.149%	$222.2246	$222.22	$222.20	$222.20
Purchase #5	$215.87	9.481%	$236.3366	$236.34	$236.35	$236.30
Purchase #6	$108.88	4.440%	$113.7143	$113.71	$113.70	$113.70
Purchase #7	$33.26	10.777%	$36.8444	$36.84	$36.85	$36.80
7 purchase totals =	$899.90		$985.5391	$985.53	$985.55	$985.40