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	$92.91	9.585%	$101.8154	$101.82	$101.80	$101.80
Purchase #2	$179.99	9.239%	$196.6193	$196.62	$196.60	$196.60
Purchase #3	$106.51	7.832%	$114.8519	$114.85	$114.85	$114.90
Purchase #4	$113.53	12.184%	$127.3625	$127.36	$127.35	$127.40
Purchase #5	$100.66	4.593%	$105.2833	$105.28	$105.30	$105.30
Purchase #6	$51.31	6.258%	$54.521	$54.52	$54.50	$54.50
Purchase #7	$204.76	10.344%	$225.9404	$225.94	$225.95	$225.90
7 purchase totals =	$849.67		$926.3938	$926.39	$926.35	$926.40