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	$242.48	13.869%	$276.1096	$276.11	$276.10	$276.10
Purchase #2	$103.53	4.372%	$108.0563	$108.06	$108.05	$108.10
Purchase #3	$183.47	12.305%	$206.046	$206.05	$206.05	$206.00
Purchase #4	$167.89	13.680%	$190.8574	$190.86	$190.85	$190.90
Purchase #5	$85.40	6.458%	$90.9151	$90.92	$90.90	$90.90
Purchase #6	$12.85	10.290%	$14.1723	$14.17	$14.15	$14.20
Purchase #7	$51.68	9.195%	$56.432	$56.43	$56.45	$56.40
7 purchase totals =	$847.30		$942.5887	$942.60	$942.55	$942.60