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	$65.83	10.549%	$72.7744	$72.77	$72.75	$72.80
Purchase #2	$220.94	8.331%	$239.3465	$239.35	$239.35	$239.30
Purchase #3	$38.81	9.603%	$42.5369	$42.54	$42.55	$42.50
Purchase #4	$58.55	13.269%	$66.319	$66.32	$66.30	$66.30
Purchase #5	$101.30	6.759%	$108.1469	$108.15	$108.15	$108.10
Purchase #6	$17.83	5.426%	$18.7975	$18.80	$18.80	$18.80
Purchase #7	$6.57	3.752%	$6.8165	$6.82	$6.80	$6.80
7 purchase totals =	$509.83		$554.7377	$554.75	$554.70	$554.60