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	$155.31	7.229%	$166.5374	$166.54	$166.55	$166.50
Purchase #2	$78.85	5.844%	$83.458	$83.46	$83.45	$83.50
Purchase #3	$137.50	4.730%	$144.0038	$144.00	$144.00	$144.00
Purchase #4	$171.72	6.615%	$183.0793	$183.08	$183.10	$183.10
Purchase #5	$210.47	9.383%	$230.2184	$230.22	$230.20	$230.20
Purchase #6	$170.38	10.523%	$188.3091	$188.31	$188.30	$188.30
Purchase #7	$75.62	10.755%	$83.7529	$83.75	$83.75	$83.80
7 purchase totals =	$999.85		$1,079.3589	$1,079.36	$1,079.35	$1,079.40