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	$28.54	3.326%	$29.4892	$29.49	$29.50	$29.50
Purchase #2	$131.40	10.677%	$145.4296	$145.43	$145.45	$145.40
Purchase #3	$139.27	3.678%	$144.3924	$144.39	$144.40	$144.40
Purchase #4	$46.95	11.111%	$52.1666	$52.17	$52.15	$52.20
Purchase #5	$217.53	11.492%	$242.5285	$242.53	$242.55	$242.50
Purchase #6	$56.79	5.630%	$59.9873	$59.99	$60.00	$60.00
Purchase #7	$21.76	11.435%	$24.2483	$24.25	$24.25	$24.20
7 purchase totals =	$642.24		$698.2419	$698.25	$698.30	$698.20