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	$150.87	10.225%	$166.2965	$166.30	$166.30	$166.30
Purchase #2	$233.91	12.409%	$262.9359	$262.94	$262.95	$262.90
Purchase #3	$159.28	10.116%	$175.3928	$175.39	$175.40	$175.40
Purchase #4	$145.52	9.241%	$158.9675	$158.97	$158.95	$159.00
Purchase #5	$107.88	9.628%	$118.2667	$118.27	$118.25	$118.30
Purchase #6	$195.55	12.293%	$219.589	$219.59	$219.60	$219.60
Purchase #7	$41.82	13.406%	$47.4264	$47.43	$47.45	$47.40
7 purchase totals =	$1,034.83		$1,148.8748	$1,148.89	$1,148.90	$1,148.90