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	$213.79	5.512%	$225.5741	$225.57	$225.55	$225.60
Purchase #2	$116.48	10.592%	$128.8176	$128.82	$128.80	$128.80
Purchase #3	$173.71	6.548%	$185.0845	$185.08	$185.10	$185.10
Purchase #4	$53.27	12.856%	$60.1184	$60.12	$60.10	$60.10
Purchase #5	$164.87	4.219%	$171.8259	$171.83	$171.85	$171.80
Purchase #6	$101.46	7.284%	$108.8503	$108.85	$108.85	$108.90
Purchase #7	$43.66	10.371%	$48.188	$48.19	$48.20	$48.20
7 purchase totals =	$867.24		$928.4588	$928.46	$928.45	$928.50