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	$36.90	6.649%	$39.3535	$39.35	$39.35	$39.40
Purchase #2	$145.74	3.553%	$150.9181	$150.92	$150.90	$150.90
Purchase #3	$118.51	7.750%	$127.6945	$127.69	$127.70	$127.70
Purchase #4	$147.27	11.259%	$163.8511	$163.85	$163.85	$163.90
Purchase #5	$166.39	3.614%	$172.4033	$172.40	$172.40	$172.40
Purchase #6	$145.99	7.258%	$156.586	$156.59	$156.60	$156.60
Purchase #7	$186.52	4.219%	$194.3893	$194.39	$194.40	$194.40
7 purchase totals =	$947.32		$1,005.1958	$1,005.19	$1,005.20	$1,005.30