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	$239.88	3.795%	$248.9834	$248.98	$249.00	$249.00
Purchase #2	$128.38	6.406%	$136.604	$136.60	$136.60	$136.60
Purchase #3	$5.38	5.321%	$5.6663	$5.67	$5.65	$5.70
Purchase #4	$94.54	6.392%	$100.583	$100.58	$100.60	$100.60
Purchase #5	$83.88	7.189%	$89.9101	$89.91	$89.90	$89.90
Purchase #6	$165.95	9.590%	$181.8646	$181.86	$181.85	$181.90
Purchase #7	$27.66	6.381%	$29.425	$29.43	$29.45	$29.40
7 purchase totals =	$745.67		$793.0364	$793.03	$793.05	$793.10