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	$62.43	12.719%	$70.3705	$70.37	$70.35	$70.40
Purchase #2	$166.58	8.312%	$180.4261	$180.43	$180.45	$180.40
Purchase #3	$193.50	10.558%	$213.9297	$213.93	$213.95	$213.90
Purchase #4	$52.59	7.346%	$56.4533	$56.45	$56.45	$56.50
Purchase #5	$55.90	6.666%	$59.6263	$59.63	$59.65	$59.60
Purchase #6	$169.92	4.757%	$178.0031	$178.00	$178.00	$178.00
Purchase #7	$153.97	5.691%	$162.7324	$162.73	$162.75	$162.70
7 purchase totals =	$854.89		$921.5414	$921.54	$921.60	$921.50