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	$56.37	9.571%	$61.7652	$61.77	$61.75	$61.80
Purchase #2	$153.92	8.523%	$167.0386	$167.04	$167.05	$167.00
Purchase #3	$29.51	11.407%	$32.8762	$32.88	$32.90	$32.90
Purchase #4	$235.56	13.687%	$267.8011	$267.80	$267.80	$267.80
Purchase #5	$34.52	7.778%	$37.205	$37.21	$37.20	$37.20
Purchase #6	$159.56	8.349%	$172.8817	$172.88	$172.90	$172.90
Purchase #7	$38.91	12.517%	$43.7804	$43.78	$43.80	$43.80
7 purchase totals =	$708.35		$783.3482	$783.36	$783.40	$783.40