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	$142.62	13.309%	$161.6013	$161.60	$161.60	$161.60
Purchase #2	$119.79	9.284%	$130.9113	$130.91	$130.90	$130.90
Purchase #3	$128.80	10.463%	$142.2763	$142.28	$142.30	$142.30
Purchase #4	$136.36	11.381%	$151.8791	$151.88	$151.90	$151.90
Purchase #5	$134.52	4.671%	$140.8034	$140.80	$140.80	$140.80
Purchase #6	$180.91	6.184%	$192.0975	$192.10	$192.10	$192.10
Purchase #7	$123.63	12.843%	$139.5078	$139.51	$139.50	$139.50
7 purchase totals =	$966.63		$1,059.0767	$1,059.08	$1,059.10	$1,059.10