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	$12.46	4.499%	$13.0206	$13.02	$13.00	$13.00
Purchase #2	$64.71	11.267%	$72.0009	$72.00	$72.00	$72.00
Purchase #3	$162.35	13.440%	$184.1698	$184.17	$184.15	$184.20
Purchase #4	$166.61	12.657%	$187.6978	$187.70	$187.70	$187.70
Purchase #5	$100.31	3.530%	$103.8509	$103.85	$103.85	$103.90
Purchase #6	$80.71	10.563%	$89.2354	$89.24	$89.25	$89.20
Purchase #7	$10.30	4.176%	$10.7301	$10.73	$10.75	$10.70
7 purchase totals =	$597.45		$660.7055	$660.71	$660.70	$660.70