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	$146.88	6.604%	$156.58	$156.58	$156.60	$156.60
Purchase #2	$117.93	7.123%	$126.3302	$126.33	$126.35	$126.30
Purchase #3	$76.25	12.169%	$85.5289	$85.53	$85.55	$85.50
Purchase #4	$149.28	3.247%	$154.1271	$154.13	$154.15	$154.10
Purchase #5	$77.33	6.717%	$82.5243	$82.52	$82.50	$82.50
Purchase #6	$78.68	10.410%	$86.8706	$86.87	$86.85	$86.90
Purchase #7	$67.94	4.609%	$71.0714	$71.07	$71.05	$71.10
7 purchase totals =	$714.29		$763.0325	$763.03	$763.05	$763.00