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	$192.28	4.295%	$200.5384	$200.54	$200.55	$200.50
Purchase #2	$219.77	9.395%	$240.4174	$240.42	$240.40	$240.40
Purchase #3	$75.82	6.118%	$80.4587	$80.46	$80.45	$80.50
Purchase #4	$140.47	8.407%	$152.2793	$152.28	$152.30	$152.30
Purchase #5	$93.42	4.364%	$97.4968	$97.50	$97.50	$97.50
Purchase #6	$219.78	5.147%	$231.0921	$231.09	$231.10	$231.10
Purchase #7	$111.80	8.239%	$121.0112	$121.01	$121.00	$121.00
7 purchase totals =	$1,053.34		$1,123.2939	$1,123.30	$1,123.30	$1,123.30