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	$89.73	12.178%	$100.6573	$100.66	$100.65	$100.70
Purchase #2	$91.92	13.774%	$104.5811	$104.58	$104.60	$104.60
Purchase #3	$19.72	8.681%	$21.4319	$21.43	$21.45	$21.40
Purchase #4	$237.38	13.715%	$269.9367	$269.94	$269.95	$269.90
Purchase #5	$198.80	12.849%	$224.3438	$224.34	$224.35	$224.30
Purchase #6	$209.63	12.243%	$235.295	$235.30	$235.30	$235.30
Purchase #7	$105.54	9.284%	$115.3383	$115.34	$115.35	$115.30
7 purchase totals =	$952.72		$1,071.5841	$1,071.59	$1,071.65	$1,071.50