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	$123.91	12.515%	$139.4173	$139.42	$139.40	$139.40
Purchase #2	$205.25	5.536%	$216.6126	$216.61	$216.60	$216.60
Purchase #3	$134.38	11.708%	$150.1132	$150.11	$150.10	$150.10
Purchase #4	$147.53	3.740%	$153.0476	$153.05	$153.05	$153.00
Purchase #5	$201.71	5.370%	$212.5418	$212.54	$212.55	$212.50
Purchase #6	$220.78	9.343%	$241.4075	$241.41	$241.40	$241.40
Purchase #7	$52.38	4.123%	$54.5396	$54.54	$54.55	$54.50
7 purchase totals =	$1,085.94		$1,167.6796	$1,167.68	$1,167.65	$1,167.50