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	$233.96	10.858%	$259.3634	$259.36	$259.35	$259.40
Purchase #2	$218.89	12.691%	$246.6693	$246.67	$246.65	$246.70
Purchase #3	$77.39	4.103%	$80.5653	$80.57	$80.55	$80.60
Purchase #4	$72.43	13.739%	$82.3812	$82.38	$82.40	$82.40
Purchase #5	$126.86	9.466%	$138.8686	$138.87	$138.85	$138.90
Purchase #6	$183.97	10.673%	$203.6051	$203.61	$203.60	$203.60
Purchase #7	$96.54	3.666%	$100.0792	$100.08	$100.10	$100.10
7 purchase totals =	$1,010.04		$1,111.5321	$1,111.54	$1,111.50	$1,111.70