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	$239.83	11.547%	$267.5232	$267.52	$267.50	$267.50
Purchase #2	$128.28	4.411%	$133.9384	$133.94	$133.95	$133.90
Purchase #3	$153.35	8.646%	$166.6086	$166.61	$166.60	$166.60
Purchase #4	$46.36	9.150%	$50.6019	$50.60	$50.60	$50.60
Purchase #5	$221.50	12.626%	$249.4666	$249.47	$249.45	$249.50
Purchase #6	$79.45	4.114%	$82.7186	$82.72	$82.70	$82.70
Purchase #7	$38.68	12.468%	$43.5026	$43.50	$43.50	$43.50
7 purchase totals =	$907.45		$994.3599	$994.36	$994.30	$994.30