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	$243.77	5.410%	$256.958	$256.96	$256.95	$257.00
Purchase #2	$16.41	9.730%	$18.0067	$18.01	$18.00	$18.00
Purchase #3	$92.69	5.163%	$97.4756	$97.48	$97.50	$97.50
Purchase #4	$221.89	9.284%	$242.4903	$242.49	$242.50	$242.50
Purchase #5	$124.94	9.865%	$137.2653	$137.27	$137.25	$137.30
Purchase #6	$93.95	10.857%	$104.1502	$104.15	$104.15	$104.20
Purchase #7	$66.76	4.864%	$70.0072	$70.01	$70.00	$70.00
7 purchase totals =	$860.41		$926.3533	$926.37	$926.35	$926.50