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	$38.93	3.723%	$40.3794	$40.38	$40.40	$40.40
Purchase #2	$43.36	10.874%	$48.075	$48.08	$48.10	$48.10
Purchase #3	$129.67	6.657%	$138.3021	$138.30	$138.30	$138.30
Purchase #4	$113.48	9.795%	$124.5954	$124.60	$124.60	$124.60
Purchase #5	$85.68	4.156%	$89.2409	$89.24	$89.25	$89.20
Purchase #6	$139.82	3.520%	$144.7417	$144.74	$144.75	$144.70
Purchase #7	$176.99	6.480%	$188.459	$188.46	$188.45	$188.50
7 purchase totals =	$727.93		$773.7935	$773.80	$773.85	$773.80