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	$113.35	12.476%	$127.4915	$127.49	$127.50	$127.50
Purchase #2	$103.39	12.409%	$116.2197	$116.22	$116.20	$116.20
Purchase #3	$58.95	7.259%	$63.2292	$63.23	$63.25	$63.20
Purchase #4	$110.28	9.357%	$120.5989	$120.60	$120.60	$120.60
Purchase #5	$188.39	4.241%	$196.3796	$196.38	$196.40	$196.40
Purchase #6	$17.73	4.389%	$18.5082	$18.51	$18.50	$18.50
Purchase #7	$231.68	7.758%	$249.6537	$249.65	$249.65	$249.70
7 purchase totals =	$823.77		$892.0808	$892.08	$892.10	$892.10