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	$189.46	13.798%	$215.6017	$215.60	$215.60	$215.60
Purchase #2	$106.86	11.321%	$118.9576	$118.96	$118.95	$119.00
Purchase #3	$90.25	12.498%	$101.5294	$101.53	$101.55	$101.50
Purchase #4	$37.78	9.669%	$41.4329	$41.43	$41.45	$41.40
Purchase #5	$144.77	5.103%	$152.1576	$152.16	$152.15	$152.20
Purchase #6	$35.41	6.726%	$37.7917	$37.79	$37.80	$37.80
Purchase #7	$84.83	5.136%	$89.1869	$89.19	$89.20	$89.20
7 purchase totals =	$689.36		$756.6578	$756.66	$756.70	$756.70