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	$19.49	4.386%	$20.3448	$20.34	$20.35	$20.30
Purchase #2	$129.64	7.858%	$139.8271	$139.83	$139.85	$139.80
Purchase #3	$159.45	8.443%	$172.9124	$172.91	$172.90	$172.90
Purchase #4	$241.79	12.245%	$271.3972	$271.40	$271.40	$271.40
Purchase #5	$32.70	10.855%	$36.2496	$36.25	$36.25	$36.20
Purchase #6	$200.51	4.147%	$208.8251	$208.83	$208.85	$208.80
Purchase #7	$228.65	9.294%	$249.9007	$249.90	$249.90	$249.90
7 purchase totals =	$1,012.23		$1,099.4569	$1,099.46	$1,099.50	$1,099.30