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	$80.78	6.611%	$86.1204	$86.12	$86.10	$86.10
Purchase #2	$84.40	8.564%	$91.628	$91.63	$91.65	$91.60
Purchase #3	$117.92	8.792%	$128.2875	$128.29	$128.30	$128.30
Purchase #4	$81.77	10.213%	$90.1212	$90.12	$90.10	$90.10
Purchase #5	$103.82	10.329%	$114.5436	$114.54	$114.55	$114.50
Purchase #6	$22.97	13.830%	$26.1468	$26.15	$26.15	$26.10
Purchase #7	$166.57	10.829%	$184.6079	$184.61	$184.60	$184.60
7 purchase totals =	$658.23		$721.4554	$721.46	$721.45	$721.30