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	$175.90	3.188%	$181.5077	$181.51	$181.50	$181.50
Purchase #2	$118.26	11.771%	$132.1804	$132.18	$132.20	$132.20
Purchase #3	$191.27	13.389%	$216.8791	$216.88	$216.90	$216.90
Purchase #4	$172.80	12.509%	$194.4156	$194.42	$194.40	$194.40
Purchase #5	$21.31	7.670%	$22.9445	$22.94	$22.95	$22.90
Purchase #6	$60.32	12.122%	$67.632	$67.63	$67.65	$67.60
Purchase #7	$80.45	4.362%	$83.9592	$83.96	$83.95	$84.00
7 purchase totals =	$820.31		$899.5185	$899.52	$899.55	$899.50