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	$132.38	3.620%	$137.1722	$137.17	$137.15	$137.20
Purchase #2	$233.79	13.558%	$265.4872	$265.49	$265.50	$265.50
Purchase #3	$30.72	7.354%	$32.9791	$32.98	$33.00	$33.00
Purchase #4	$198.61	13.474%	$225.3707	$225.37	$225.35	$225.40
Purchase #5	$176.65	11.444%	$196.8658	$196.87	$196.85	$196.90
Purchase #6	$37.37	3.296%	$38.6017	$38.60	$38.60	$38.60
Purchase #7	$175.29	5.107%	$184.2421	$184.24	$184.25	$184.20
7 purchase totals =	$984.81		$1,080.7188	$1,080.72	$1,080.70	$1,080.80