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	$38.69	5.257%	$40.7239	$40.72	$40.70	$40.70
Purchase #2	$57.91	4.656%	$60.6063	$60.61	$60.60	$60.60
Purchase #3	$250.86	12.695%	$282.7067	$282.71	$282.70	$282.70
Purchase #4	$71.38	13.577%	$81.0713	$81.07	$81.05	$81.10
Purchase #5	$134.42	7.415%	$144.3872	$144.39	$144.40	$144.40
Purchase #6	$96.59	6.724%	$103.0847	$103.08	$103.10	$103.10
Purchase #7	$234.29	4.292%	$244.3457	$244.35	$244.35	$244.30
7 purchase totals =	$884.14		$956.9258	$956.93	$956.90	$956.90