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	$228.56	13.389%	$259.1619	$259.16	$259.15	$259.20
Purchase #2	$240.51	11.828%	$268.9575	$268.96	$268.95	$269.00
Purchase #3	$115.39	11.717%	$128.9102	$128.91	$128.90	$128.90
Purchase #4	$217.42	3.436%	$224.8906	$224.89	$224.90	$224.90
Purchase #5	$112.54	13.690%	$127.9467	$127.95	$127.95	$127.90
Purchase #6	$127.82	9.421%	$139.8619	$139.86	$139.85	$139.90
Purchase #7	$248.57	10.768%	$275.336	$275.34	$275.35	$275.30
7 purchase totals =	$1,290.81		$1,425.0648	$1,425.07	$1,425.05	$1,425.10