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	$156.61	13.713%	$178.0859	$178.09	$178.10	$178.10
Purchase #2	$115.89	6.594%	$123.5318	$123.53	$123.55	$123.50
Purchase #3	$211.67	9.547%	$231.8781	$231.88	$231.90	$231.90
Purchase #4	$71.32	12.386%	$80.1537	$80.15	$80.15	$80.20
Purchase #5	$199.64	9.273%	$218.1526	$218.15	$218.15	$218.20
Purchase #6	$192.34	4.208%	$200.4337	$200.43	$200.45	$200.40
Purchase #7	$194.41	12.810%	$219.3139	$219.31	$219.30	$219.30
7 purchase totals =	$1,141.88		$1,251.5497	$1,251.54	$1,251.60	$1,251.60