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	$26.78	10.475%	$29.5852	$29.59	$29.60	$29.60
Purchase #2	$85.57	3.488%	$88.5547	$88.55	$88.55	$88.60
Purchase #3	$56.70	5.301%	$59.7057	$59.71	$59.70	$59.70
Purchase #4	$58.42	5.805%	$61.8113	$61.81	$61.80	$61.80
Purchase #5	$29.75	11.506%	$33.173	$33.17	$33.15	$33.20
Purchase #6	$135.95	6.708%	$145.0695	$145.07	$145.05	$145.10
Purchase #7	$100.39	11.735%	$112.1708	$112.17	$112.15	$112.20
7 purchase totals =	$493.56		$530.0702	$530.07	$530.00	$530.20