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	$34.79	9.604%	$38.1312	$38.13	$38.15	$38.10
Purchase #2	$153.60	10.346%	$169.4915	$169.49	$169.50	$169.50
Purchase #3	$114.70	4.218%	$119.538	$119.54	$119.55	$119.50
Purchase #4	$241.45	3.598%	$250.1374	$250.14	$250.15	$250.10
Purchase #5	$148.78	11.429%	$165.7841	$165.78	$165.80	$165.80
Purchase #6	$182.70	4.791%	$191.4532	$191.45	$191.45	$191.50
Purchase #7	$83.82	10.298%	$92.4518	$92.45	$92.45	$92.50
7 purchase totals =	$959.84		$1,026.9872	$1,026.98	$1,027.05	$1,027.00