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	$250.94	11.416%	$279.5873	$279.59	$279.60	$279.60
Purchase #2	$238.59	13.200%	$270.0839	$270.08	$270.10	$270.10
Purchase #3	$203.61	7.141%	$218.1498	$218.15	$218.15	$218.10
Purchase #4	$238.79	4.542%	$249.6358	$249.64	$249.65	$249.60
Purchase #5	$154.93	11.256%	$172.3689	$172.37	$172.35	$172.40
Purchase #6	$125.77	4.842%	$131.8598	$131.86	$131.85	$131.90
Purchase #7	$111.85	5.847%	$118.3899	$118.39	$118.40	$118.40
7 purchase totals =	$1,324.48		$1,440.0754	$1,440.08	$1,440.10	$1,440.10