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	$166.65	3.288%	$172.1295	$172.13	$172.15	$172.10
Purchase #2	$100.58	3.490%	$104.0902	$104.09	$104.10	$104.10
Purchase #3	$106.29	10.423%	$117.3686	$117.37	$117.35	$117.40
Purchase #4	$211.51	12.283%	$237.4898	$237.49	$237.50	$237.50
Purchase #5	$38.95	12.226%	$43.712	$43.71	$43.70	$43.70
Purchase #6	$108.35	7.359%	$116.3235	$116.32	$116.30	$116.30
Purchase #7	$130.90	10.601%	$144.7767	$144.78	$144.80	$144.80
7 purchase totals =	$863.23		$935.8903	$935.89	$935.90	$935.90