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	$48.82	12.379%	$54.8634	$54.86	$54.85	$54.90
Purchase #2	$154.81	9.625%	$169.7105	$169.71	$169.70	$169.70
Purchase #3	$163.73	5.475%	$172.6942	$172.69	$172.70	$172.70
Purchase #4	$40.28	7.666%	$43.3679	$43.37	$43.35	$43.40
Purchase #5	$39.72	4.420%	$41.4756	$41.48	$41.50	$41.50
Purchase #6	$166.79	11.333%	$185.6923	$185.69	$185.70	$185.70
Purchase #7	$75.70	13.110%	$85.6243	$85.62	$85.60	$85.60
7 purchase totals =	$689.85		$753.4282	$753.42	$753.40	$753.50