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	$65.73	4.228%	$68.5091	$68.51	$68.50	$68.50
Purchase #2	$209.81	8.694%	$228.0509	$228.05	$228.05	$228.10
Purchase #3	$103.50	8.327%	$112.1184	$112.12	$112.10	$112.10
Purchase #4	$103.65	3.123%	$106.887	$106.89	$106.90	$106.90
Purchase #5	$81.59	9.267%	$89.1509	$89.15	$89.15	$89.20
Purchase #6	$160.26	4.476%	$167.4332	$167.43	$167.45	$167.40
Purchase #7	$32.56	5.393%	$34.316	$34.32	$34.30	$34.30
7 purchase totals =	$757.10		$806.4655	$806.47	$806.45	$806.50