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	$230.69	3.818%	$239.4977	$239.50	$239.50	$239.50
Purchase #2	$142.86	11.198%	$158.8575	$158.86	$158.85	$158.90
Purchase #3	$57.75	6.321%	$61.4004	$61.40	$61.40	$61.40
Purchase #4	$235.79	12.544%	$265.3675	$265.37	$265.35	$265.40
Purchase #5	$10.69	5.567%	$11.2851	$11.29	$11.30	$11.30
Purchase #6	$145.85	9.821%	$160.1739	$160.17	$160.15	$160.20
Purchase #7	$164.75	11.368%	$183.4788	$183.48	$183.50	$183.50
7 purchase totals =	$988.38		$1,080.0609	$1,080.07	$1,080.05	$1,080.20