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	$21.29	12.677%	$23.9889	$23.99	$24.00	$24.00
Purchase #2	$156.41	9.862%	$171.8352	$171.84	$171.85	$171.80
Purchase #3	$198.95	9.431%	$217.713	$217.71	$217.70	$217.70
Purchase #4	$53.67	10.240%	$59.1658	$59.17	$59.15	$59.20
Purchase #5	$98.26	13.595%	$111.6184	$111.62	$111.60	$111.60
Purchase #6	$181.56	11.836%	$203.0494	$203.05	$203.05	$203.00
Purchase #7	$243.90	12.389%	$274.1168	$274.12	$274.10	$274.10
7 purchase totals =	$954.04		$1,061.4875	$1,061.50	$1,061.45	$1,061.40