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	$17.55	5.722%	$18.5542	$18.55	$18.55	$18.60
Purchase #2	$101.83	3.636%	$105.5325	$105.53	$105.55	$105.50
Purchase #3	$26.34	7.175%	$28.2299	$28.23	$28.25	$28.20
Purchase #4	$144.52	10.666%	$159.9345	$159.93	$159.95	$159.90
Purchase #5	$16.60	11.274%	$18.4715	$18.47	$18.45	$18.50
Purchase #6	$124.93	13.569%	$141.8818	$141.88	$141.90	$141.90
Purchase #7	$49.59	13.583%	$56.3258	$56.33	$56.35	$56.30
7 purchase totals =	$481.36		$528.9302	$528.92	$529.00	$528.90