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	$80.54	11.550%	$89.8424	$89.84	$89.85	$89.80
Purchase #2	$57.88	8.773%	$62.9578	$62.96	$62.95	$63.00
Purchase #3	$137.35	12.745%	$154.8553	$154.86	$154.85	$154.90
Purchase #4	$130.65	11.264%	$145.3664	$145.37	$145.35	$145.40
Purchase #5	$127.27	3.523%	$131.7537	$131.75	$131.75	$131.80
Purchase #6	$234.29	6.544%	$249.6219	$249.62	$249.60	$249.60
Purchase #7	$63.41	4.474%	$66.247	$66.25	$66.25	$66.20
7 purchase totals =	$831.39		$900.6445	$900.65	$900.60	$900.70