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	$161.43	11.163%	$179.4504	$179.45	$179.45	$179.50
Purchase #2	$207.57	7.503%	$223.144	$223.14	$223.15	$223.10
Purchase #3	$130.58	11.537%	$145.645	$145.65	$145.65	$145.60
Purchase #4	$50.80	11.168%	$56.4733	$56.47	$56.45	$56.50
Purchase #5	$200.55	5.513%	$211.6063	$211.61	$211.60	$211.60
Purchase #6	$39.71	4.487%	$41.4918	$41.49	$41.50	$41.50
Purchase #7	$81.78	4.424%	$85.3979	$85.40	$85.40	$85.40
7 purchase totals =	$872.42		$943.2087	$943.21	$943.20	$943.20