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	$33.82	12.503%	$38.0485	$38.05	$38.05	$38.00
Purchase #2	$180.33	10.531%	$199.3206	$199.32	$199.30	$199.30
Purchase #3	$115.94	13.269%	$131.3241	$131.32	$131.30	$131.30
Purchase #4	$18.84	11.328%	$20.9742	$20.97	$20.95	$21.00
Purchase #5	$59.80	10.685%	$66.1896	$66.19	$66.20	$66.20
Purchase #6	$13.82	12.545%	$15.5537	$15.55	$15.55	$15.60
Purchase #7	$215.46	3.403%	$222.7921	$222.79	$222.80	$222.80
7 purchase totals =	$638.01		$694.2028	$694.19	$694.15	$694.20