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	$34.89	10.278%	$38.476	$38.48	$38.50	$38.50
Purchase #2	$125.71	7.123%	$134.6643	$134.66	$134.65	$134.70
Purchase #3	$121.42	5.726%	$128.3725	$128.37	$128.35	$128.40
Purchase #4	$79.88	3.347%	$82.5536	$82.55	$82.55	$82.60
Purchase #5	$115.40	10.154%	$127.1177	$127.12	$127.10	$127.10
Purchase #6	$114.28	4.412%	$119.322	$119.32	$119.30	$119.30
Purchase #7	$86.69	11.396%	$96.5692	$96.57	$96.55	$96.60
7 purchase totals =	$678.27		$727.0753	$727.07	$727.00	$727.20