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	$155.55	3.185%	$160.5043	$160.50	$160.50	$160.50
Purchase #2	$61.36	10.569%	$67.8451	$67.85	$67.85	$67.80
Purchase #3	$85.26	4.184%	$88.8273	$88.83	$88.85	$88.80
Purchase #4	$123.48	12.607%	$139.0471	$139.05	$139.05	$139.00
Purchase #5	$246.45	11.807%	$275.5484	$275.55	$275.55	$275.50
Purchase #6	$113.40	12.142%	$127.169	$127.17	$127.15	$127.20
Purchase #7	$34.25	9.248%	$37.4174	$37.42	$37.40	$37.40
7 purchase totals =	$819.75		$896.3586	$896.37	$896.35	$896.20