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	$5.78	6.360%	$6.1476	$6.15	$6.15	$6.10
Purchase #2	$141.56	7.325%	$151.9293	$151.93	$151.95	$151.90
Purchase #3	$91.27	11.632%	$101.8865	$101.89	$101.90	$101.90
Purchase #4	$51.42	6.326%	$54.6728	$54.67	$54.65	$54.70
Purchase #5	$128.73	8.672%	$139.8935	$139.89	$139.90	$139.90
Purchase #6	$138.67	4.598%	$145.046	$145.05	$145.05	$145.00
Purchase #7	$112.79	9.123%	$123.0798	$123.08	$123.10	$123.10
7 purchase totals =	$670.22		$722.6555	$722.66	$722.70	$722.60