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	$170.42	13.758%	$193.8664	$193.87	$193.85	$193.90
Purchase #2	$174.38	12.710%	$196.5437	$196.54	$196.55	$196.50
Purchase #3	$56.97	12.152%	$63.893	$63.89	$63.90	$63.90
Purchase #4	$109.91	7.487%	$118.139	$118.14	$118.15	$118.10
Purchase #5	$12.25	7.302%	$13.1445	$13.14	$13.15	$13.10
Purchase #6	$162.90	10.476%	$179.9654	$179.97	$179.95	$180.00
Purchase #7	$45.95	9.734%	$50.4228	$50.42	$50.40	$50.40
7 purchase totals =	$732.78		$815.9748	$815.97	$815.95	$815.90