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	$98.76	9.243%	$107.8884	$107.89	$107.90	$107.90
Purchase #2	$100.32	6.261%	$106.601	$106.60	$106.60	$106.60
Purchase #3	$148.84	12.236%	$167.0521	$167.05	$167.05	$167.10
Purchase #4	$171.39	13.395%	$194.3477	$194.35	$194.35	$194.30
Purchase #5	$183.54	3.661%	$190.2594	$190.26	$190.25	$190.30
Purchase #6	$72.50	8.628%	$78.7553	$78.76	$78.75	$78.80
Purchase #7	$71.68	3.128%	$73.9222	$73.92	$73.90	$73.90
7 purchase totals =	$847.03		$918.8261	$918.83	$918.80	$918.90