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	$67.65	7.601%	$72.7921	$72.79	$72.80	$72.80
Purchase #2	$211.38	13.670%	$240.2756	$240.28	$240.30	$240.30
Purchase #3	$121.33	10.863%	$134.5101	$134.51	$134.50	$134.50
Purchase #4	$154.65	3.697%	$160.3674	$160.37	$160.35	$160.40
Purchase #5	$75.37	4.312%	$78.62	$78.62	$78.60	$78.60
Purchase #6	$84.66	4.339%	$88.3334	$88.33	$88.35	$88.30
Purchase #7	$103.82	9.381%	$113.5594	$113.56	$113.55	$113.60
7 purchase totals =	$818.86		$888.4580	$888.46	$888.45	$888.50