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	$20.73	3.350%	$21.4245	$21.42	$21.40	$21.40
Purchase #2	$121.40	4.733%	$127.1459	$127.15	$127.15	$127.10
Purchase #3	$48.56	8.666%	$52.7682	$52.77	$52.75	$52.80
Purchase #4	$239.81	8.387%	$259.9229	$259.92	$259.90	$259.90
Purchase #5	$24.95	13.700%	$28.3682	$28.37	$28.35	$28.40
Purchase #6	$151.45	10.524%	$167.3886	$167.39	$167.40	$167.40
Purchase #7	$71.87	11.354%	$80.0301	$80.03	$80.05	$80.00
7 purchase totals =	$678.77		$737.0484	$737.05	$737.00	$737.00