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	$66.50	5.233%	$69.9799	$69.98	$70.00	$70.00
Purchase #2	$192.60	11.359%	$214.4774	$214.48	$214.50	$214.50
Purchase #3	$168.82	10.360%	$186.3098	$186.31	$186.30	$186.30
Purchase #4	$166.93	4.789%	$174.9243	$174.92	$174.90	$174.90
Purchase #5	$35.82	10.150%	$39.4557	$39.46	$39.45	$39.50
Purchase #6	$62.32	4.576%	$65.1718	$65.17	$65.15	$65.20
Purchase #7	$107.85	10.773%	$119.4687	$119.47	$119.45	$119.50
7 purchase totals =	$800.84		$869.7876	$869.79	$869.75	$869.90