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	$68.64	12.590%	$77.2818	$77.28	$77.30	$77.30
Purchase #2	$29.57	5.178%	$31.1011	$31.10	$31.10	$31.10
Purchase #3	$176.78	6.788%	$188.7798	$188.78	$188.80	$188.80
Purchase #4	$48.32	12.727%	$54.4697	$54.47	$54.45	$54.50
Purchase #5	$127.78	8.844%	$139.0809	$139.08	$139.10	$139.10
Purchase #6	$125.90	6.837%	$134.5078	$134.51	$134.50	$134.50
Purchase #7	$168.70	13.120%	$190.8334	$190.83	$190.85	$190.80
7 purchase totals =	$745.69		$816.0545	$816.05	$816.10	$816.10