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	$103.46	5.733%	$109.3914	$109.39	$109.40	$109.40
Purchase #2	$127.91	11.860%	$143.0801	$143.08	$143.10	$143.10
Purchase #3	$228.50	13.587%	$259.5463	$259.55	$259.55	$259.50
Purchase #4	$56.86	13.709%	$64.6549	$64.65	$64.65	$64.70
Purchase #5	$214.50	13.367%	$243.1722	$243.17	$243.15	$243.20
Purchase #6	$165.95	3.675%	$172.0487	$172.05	$172.05	$172.00
Purchase #7	$32.85	12.239%	$36.8705	$36.87	$36.85	$36.90
7 purchase totals =	$930.03		$1,028.7641	$1,028.76	$1,028.75	$1,028.80