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	$60.71	12.533%	$68.3188	$68.32	$68.30	$68.30
Purchase #2	$99.47	13.124%	$112.5244	$112.52	$112.50	$112.50
Purchase #3	$123.83	5.255%	$130.3373	$130.34	$130.35	$130.30
Purchase #4	$147.42	12.612%	$166.0126	$166.01	$166.00	$166.00
Purchase #5	$250.81	13.284%	$284.1276	$284.13	$284.15	$284.10
Purchase #6	$58.47	9.231%	$63.8674	$63.87	$63.85	$63.90
Purchase #7	$84.87	7.154%	$90.9416	$90.94	$90.95	$90.90
7 purchase totals =	$825.58		$916.1297	$916.13	$916.10	$916.00