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	$70.33	13.579%	$79.8801	$79.88	$79.90	$79.90
Purchase #2	$111.93	13.785%	$127.3596	$127.36	$127.35	$127.40
Purchase #3	$136.92	3.420%	$141.6027	$141.60	$141.60	$141.60
Purchase #4	$173.90	6.685%	$185.5252	$185.53	$185.55	$185.50
Purchase #5	$7.51	7.600%	$8.0808	$8.08	$8.10	$8.10
Purchase #6	$170.63	8.178%	$184.5841	$184.58	$184.60	$184.60
Purchase #7	$139.50	13.571%	$158.4315	$158.43	$158.45	$158.40
7 purchase totals =	$810.72		$885.4640	$885.46	$885.55	$885.50