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	$81.43	4.531%	$85.1196	$85.12	$85.10	$85.10
Purchase #2	$163.62	9.665%	$179.4339	$179.43	$179.45	$179.40
Purchase #3	$51.43	9.509%	$56.3205	$56.32	$56.30	$56.30
Purchase #4	$20.60	6.283%	$21.8943	$21.89	$21.90	$21.90
Purchase #5	$99.43	10.830%	$110.1983	$110.20	$110.20	$110.20
Purchase #6	$185.66	4.593%	$194.1874	$194.19	$194.20	$194.20
Purchase #7	$123.84	12.527%	$139.3534	$139.35	$139.35	$139.40
7 purchase totals =	$726.01		$786.5074	$786.50	$786.50	$786.50