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	$175.32	13.375%	$198.7691	$198.77	$198.75	$198.80
Purchase #2	$122.30	12.492%	$137.5777	$137.58	$137.60	$137.60
Purchase #3	$84.46	4.246%	$88.0462	$88.05	$88.05	$88.00
Purchase #4	$109.51	12.608%	$123.317	$123.32	$123.30	$123.30
Purchase #5	$59.64	5.463%	$62.8981	$62.90	$62.90	$62.90
Purchase #6	$194.68	12.260%	$218.5478	$218.55	$218.55	$218.50
Purchase #7	$128.31	12.503%	$144.3526	$144.35	$144.35	$144.40
7 purchase totals =	$874.22		$973.5085	$973.52	$973.50	$973.50