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	$128.89	6.336%	$137.0565	$137.06	$137.05	$137.10
Purchase #2	$95.88	3.503%	$99.2387	$99.24	$99.25	$99.20
Purchase #3	$107.62	3.488%	$111.3738	$111.37	$111.35	$111.40
Purchase #4	$233.92	10.504%	$258.491	$258.49	$258.50	$258.50
Purchase #5	$32.96	4.642%	$34.49	$34.49	$34.50	$34.50
Purchase #6	$8.28	3.345%	$8.557	$8.56	$8.55	$8.60
Purchase #7	$107.70	10.367%	$118.8653	$118.87	$118.85	$118.90
7 purchase totals =	$715.25		$768.0723	$768.08	$768.05	$768.20