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	$242.36	9.458%	$265.2824	$265.28	$265.30	$265.30
Purchase #2	$192.84	3.619%	$199.8189	$199.82	$199.80	$199.80
Purchase #3	$241.54	5.526%	$254.8875	$254.89	$254.90	$254.90
Purchase #4	$124.65	11.838%	$139.4061	$139.41	$139.40	$139.40
Purchase #5	$23.69	5.171%	$24.915	$24.92	$24.90	$24.90
Purchase #6	$55.34	4.572%	$57.8701	$57.87	$57.85	$57.90
Purchase #7	$78.79	13.550%	$89.466	$89.47	$89.45	$89.50
7 purchase totals =	$959.21		$1,031.6460	$1,031.66	$1,031.60	$1,031.70