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	$74.38	11.394%	$82.8549	$82.85	$82.85	$82.90
Purchase #2	$126.52	13.466%	$143.5572	$143.56	$143.55	$143.60
Purchase #3	$92.53	8.317%	$100.2257	$100.23	$100.25	$100.20
Purchase #4	$36.79	10.780%	$40.756	$40.76	$40.75	$40.80
Purchase #5	$51.27	7.403%	$55.0655	$55.07	$55.05	$55.10
Purchase #6	$233.37	12.422%	$262.3592	$262.36	$262.35	$262.40
Purchase #7	$64.25	3.239%	$66.3311	$66.33	$66.35	$66.30
7 purchase totals =	$679.11		$751.1496	$751.16	$751.15	$751.30