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	$27.52	13.452%	$31.222	$31.22	$31.20	$31.20
Purchase #2	$123.51	11.638%	$137.8841	$137.88	$137.90	$137.90
Purchase #3	$134.55	12.850%	$151.8397	$151.84	$151.85	$151.80
Purchase #4	$178.26	10.373%	$196.7509	$196.75	$196.75	$196.80
Purchase #5	$122.27	8.752%	$132.9711	$132.97	$132.95	$133.00
Purchase #6	$172.99	8.164%	$187.1129	$187.11	$187.10	$187.10
Purchase #7	$39.84	8.307%	$43.1495	$43.15	$43.15	$43.10
7 purchase totals =	$798.94		$880.9302	$880.92	$880.90	$880.90