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	$163.53	12.851%	$184.5452	$184.55	$184.55	$184.50
Purchase #2	$232.34	6.844%	$248.2413	$248.24	$248.25	$248.20
Purchase #3	$166.29	9.226%	$181.6319	$181.63	$181.65	$181.60
Purchase #4	$100.45	13.379%	$113.8892	$113.89	$113.90	$113.90
Purchase #5	$216.32	5.221%	$227.6141	$227.61	$227.60	$227.60
Purchase #6	$15.90	10.140%	$17.5123	$17.51	$17.50	$17.50
Purchase #7	$111.60	4.715%	$116.8619	$116.86	$116.85	$116.90
7 purchase totals =	$1,006.43		$1,090.2959	$1,090.29	$1,090.30	$1,090.20