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	$93.73	10.233%	$103.3214	$103.32	$103.30	$103.30
Purchase #2	$27.53	5.810%	$29.1295	$29.13	$29.15	$29.10
Purchase #3	$70.42	13.443%	$79.8866	$79.89	$79.90	$79.90
Purchase #4	$55.47	7.502%	$59.6314	$59.63	$59.65	$59.60
Purchase #5	$220.93	13.421%	$250.581	$250.58	$250.60	$250.60
Purchase #6	$49.79	3.198%	$51.3823	$51.38	$51.40	$51.40
Purchase #7	$121.90	7.837%	$131.4533	$131.45	$131.45	$131.50
7 purchase totals =	$639.77		$705.3855	$705.38	$705.45	$705.40