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	$113.99	12.789%	$128.5682	$128.57	$128.55	$128.60
Purchase #2	$11.63	8.536%	$12.6227	$12.62	$12.60	$12.60
Purchase #3	$176.25	7.718%	$189.853	$189.85	$189.85	$189.90
Purchase #4	$133.56	4.342%	$139.3592	$139.36	$139.35	$139.40
Purchase #5	$248.33	5.684%	$262.4451	$262.45	$262.45	$262.40
Purchase #6	$120.36	5.770%	$127.3048	$127.30	$127.30	$127.30
Purchase #7	$250.81	12.314%	$281.6947	$281.69	$281.70	$281.70
7 purchase totals =	$1,054.93		$1,141.8477	$1,141.84	$1,141.80	$1,141.90