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	$34.50	11.121%	$38.3367	$38.34	$38.35	$38.30
Purchase #2	$49.59	3.110%	$51.1322	$51.13	$51.15	$51.10
Purchase #3	$132.56	7.304%	$142.2422	$142.24	$142.25	$142.20
Purchase #4	$31.97	3.260%	$33.0122	$33.01	$33.00	$33.00
Purchase #5	$96.25	12.351%	$108.1378	$108.14	$108.15	$108.10
Purchase #6	$17.86	3.501%	$18.4853	$18.49	$18.50	$18.50
Purchase #7	$19.83	5.133%	$20.8479	$20.85	$20.85	$20.80
7 purchase totals =	$382.56		$412.1943	$412.20	$412.25	$412.00