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	$78.56	6.794%	$83.8974	$83.90	$83.90	$83.90
Purchase #2	$71.95	7.766%	$77.5376	$77.54	$77.55	$77.50
Purchase #3	$245.26	8.540%	$266.2052	$266.21	$266.20	$266.20
Purchase #4	$29.60	7.607%	$31.8517	$31.85	$31.85	$31.90
Purchase #5	$72.49	4.687%	$75.8876	$75.89	$75.90	$75.90
Purchase #6	$16.89	3.619%	$17.5012	$17.50	$17.50	$17.50
Purchase #7	$105.83	9.868%	$116.2733	$116.27	$116.25	$116.30
7 purchase totals =	$620.58		$669.1540	$669.16	$669.15	$669.20