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	$74.42	11.289%	$82.8213	$82.82	$82.80	$82.80
Purchase #2	$173.68	11.874%	$194.3028	$194.30	$194.30	$194.30
Purchase #3	$153.53	4.143%	$159.8907	$159.89	$159.90	$159.90
Purchase #4	$80.35	12.285%	$90.221	$90.22	$90.20	$90.20
Purchase #5	$107.96	6.149%	$114.5985	$114.60	$114.60	$114.60
Purchase #6	$70.99	8.722%	$77.1817	$77.18	$77.20	$77.20
Purchase #7	$149.94	8.593%	$162.8243	$162.82	$162.80	$162.80
7 purchase totals =	$810.87		$881.8403	$881.83	$881.80	$881.80