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	$13.36	9.503%	$14.6296	$14.63	$14.65	$14.60
Purchase #2	$146.44	3.675%	$151.8217	$151.82	$151.80	$151.80
Purchase #3	$142.52	8.674%	$154.8822	$154.88	$154.90	$154.90
Purchase #4	$33.95	13.552%	$38.5509	$38.55	$38.55	$38.60
Purchase #5	$121.47	5.862%	$128.5906	$128.59	$128.60	$128.60
Purchase #6	$29.69	5.526%	$31.3307	$31.33	$31.35	$31.30
Purchase #7	$145.30	9.290%	$158.7984	$158.80	$158.80	$158.80
7 purchase totals =	$632.73		$678.6041	$678.60	$678.65	$678.60