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	$95.63	11.810%	$106.9239	$106.92	$106.90	$106.90
Purchase #2	$82.49	6.351%	$87.7289	$87.73	$87.75	$87.70
Purchase #3	$89.51	5.166%	$94.1341	$94.13	$94.15	$94.10
Purchase #4	$75.47	4.163%	$78.6118	$78.61	$78.60	$78.60
Purchase #5	$250.74	11.328%	$279.1438	$279.14	$279.15	$279.10
Purchase #6	$5.73	12.832%	$6.4653	$6.47	$6.45	$6.50
Purchase #7	$99.44	4.109%	$103.526	$103.53	$103.55	$103.50
7 purchase totals =	$699.01		$756.5338	$756.53	$756.55	$756.40