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	$127.99	9.142%	$139.6908	$139.69	$139.70	$139.70
Purchase #2	$231.28	13.546%	$262.6092	$262.61	$262.60	$262.60
Purchase #3	$34.51	11.769%	$38.5715	$38.57	$38.55	$38.60
Purchase #4	$244.82	10.692%	$270.9962	$271.00	$271.00	$271.00
Purchase #5	$54.53	3.792%	$56.5978	$56.60	$56.60	$56.60
Purchase #6	$38.66	12.684%	$43.5636	$43.56	$43.55	$43.60
Purchase #7	$82.40	11.678%	$92.0227	$92.02	$92.00	$92.00
7 purchase totals =	$814.19		$904.0518	$904.05	$904.00	$904.10