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	$24.81	9.172%	$27.0856	$27.09	$27.10	$27.10
Purchase #2	$81.74	10.120%	$90.0121	$90.01	$90.00	$90.00
Purchase #3	$205.59	6.488%	$218.9287	$218.93	$218.95	$218.90
Purchase #4	$86.47	3.840%	$89.7904	$89.79	$89.80	$89.80
Purchase #5	$177.60	12.740%	$200.2262	$200.23	$200.25	$200.20
Purchase #6	$38.99	10.204%	$42.9685	$42.97	$42.95	$43.00
Purchase #7	$92.53	13.545%	$105.0632	$105.06	$105.05	$105.10
7 purchase totals =	$707.73		$774.0747	$774.08	$774.10	$774.10