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	$175.28	5.817%	$185.476	$185.48	$185.50	$185.50
Purchase #2	$164.67	9.261%	$179.9201	$179.92	$179.90	$179.90
Purchase #3	$71.67	13.615%	$81.4279	$81.43	$81.45	$81.40
Purchase #4	$24.52	10.246%	$27.0323	$27.03	$27.05	$27.00
Purchase #5	$122.71	9.403%	$134.2484	$134.25	$134.25	$134.20
Purchase #6	$67.48	7.579%	$72.5943	$72.59	$72.60	$72.60
Purchase #7	$116.27	9.645%	$127.4842	$127.48	$127.50	$127.50
7 purchase totals =	$742.60		$808.1832	$808.18	$808.25	$808.10