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	$81.79	10.862%	$90.674	$90.67	$90.65	$90.70
Purchase #2	$62.31	13.410%	$70.6658	$70.67	$70.65	$70.70
Purchase #3	$126.35	10.697%	$139.8657	$139.87	$139.85	$139.90
Purchase #4	$42.28	13.856%	$48.1383	$48.14	$48.15	$48.10
Purchase #5	$211.35	7.550%	$227.3069	$227.31	$227.30	$227.30
Purchase #6	$250.63	13.431%	$284.2921	$284.29	$284.30	$284.30
Purchase #7	$60.43	8.612%	$65.6342	$65.63	$65.65	$65.60
7 purchase totals =	$835.14		$926.5770	$926.58	$926.55	$926.60