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	$144.52	10.724%	$160.0183	$160.02	$160.00	$160.00
Purchase #2	$174.53	8.128%	$188.7158	$188.72	$188.70	$188.70
Purchase #3	$218.93	4.296%	$228.3352	$228.34	$228.35	$228.30
Purchase #4	$136.40	8.681%	$148.2409	$148.24	$148.25	$148.20
Purchase #5	$90.88	9.191%	$99.2328	$99.23	$99.25	$99.20
Purchase #6	$101.92	11.173%	$113.3075	$113.31	$113.30	$113.30
Purchase #7	$126.85	10.301%	$139.9168	$139.92	$139.90	$139.90
7 purchase totals =	$994.03		$1,077.7673	$1,077.78	$1,077.75	$1,077.60