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	$64.83	9.229%	$70.8132	$70.81	$70.80	$70.80
Purchase #2	$74.84	4.226%	$78.0027	$78.00	$78.00	$78.00
Purchase #3	$239.85	9.619%	$262.9212	$262.92	$262.90	$262.90
Purchase #4	$171.31	10.350%	$189.0406	$189.04	$189.05	$189.00
Purchase #5	$131.35	6.145%	$139.4215	$139.42	$139.40	$139.40
Purchase #6	$22.59	10.329%	$24.9233	$24.92	$24.90	$24.90
Purchase #7	$90.62	9.493%	$99.2226	$99.22	$99.20	$99.20
7 purchase totals =	$795.39		$864.3451	$864.33	$864.25	$864.20