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	$123.28	10.506%	$136.2318	$136.23	$136.25	$136.20
Purchase #2	$70.81	7.464%	$76.0953	$76.10	$76.10	$76.10
Purchase #3	$124.63	10.295%	$137.4607	$137.46	$137.45	$137.50
Purchase #4	$78.25	4.522%	$81.7885	$81.79	$81.80	$81.80
Purchase #5	$143.70	5.250%	$151.2443	$151.24	$151.25	$151.20
Purchase #6	$160.87	7.212%	$172.4719	$172.47	$172.45	$172.50
Purchase #7	$57.87	6.214%	$61.466	$61.47	$61.45	$61.50
7 purchase totals =	$759.41		$816.7585	$816.76	$816.75	$816.80