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	$34.90	11.256%	$38.8283	$38.83	$38.85	$38.80
Purchase #2	$191.60	4.677%	$200.5611	$200.56	$200.55	$200.60
Purchase #3	$18.39	7.110%	$19.6975	$19.70	$19.70	$19.70
Purchase #4	$194.76	7.810%	$209.9708	$209.97	$209.95	$210.00
Purchase #5	$179.29	12.410%	$201.5399	$201.54	$201.55	$201.50
Purchase #6	$134.72	11.714%	$150.5011	$150.50	$150.50	$150.50
Purchase #7	$108.46	10.216%	$119.5403	$119.54	$119.55	$119.50
7 purchase totals =	$862.12		$940.6390	$940.64	$940.65	$940.60