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	$67.36	13.123%	$76.1997	$76.20	$76.20	$76.20
Purchase #2	$49.71	11.493%	$55.4232	$55.42	$55.40	$55.40
Purchase #3	$139.65	8.603%	$151.6641	$151.66	$151.65	$151.70
Purchase #4	$11.66	5.691%	$12.3236	$12.32	$12.30	$12.30
Purchase #5	$188.87	7.551%	$203.1316	$203.13	$203.15	$203.10
Purchase #6	$181.86	10.156%	$200.3297	$200.33	$200.35	$200.30
Purchase #7	$246.27	13.499%	$279.514	$279.51	$279.50	$279.50
7 purchase totals =	$885.38		$978.5859	$978.57	$978.55	$978.50