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	$238.49	3.125%	$245.9428	$245.94	$245.95	$245.90
Purchase #2	$110.44	11.423%	$123.0556	$123.06	$123.05	$123.10
Purchase #3	$218.31	13.833%	$248.5088	$248.51	$248.50	$248.50
Purchase #4	$250.99	13.377%	$284.5649	$284.56	$284.55	$284.60
Purchase #5	$46.25	4.736%	$48.4404	$48.44	$48.45	$48.40
Purchase #6	$232.71	9.836%	$255.5994	$255.60	$255.60	$255.60
Purchase #7	$85.93	9.584%	$94.1655	$94.17	$94.15	$94.20
7 purchase totals =	$1,183.12		$1,300.2774	$1,300.28	$1,300.25	$1,300.30