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	$179.31	4.549%	$187.4668	$187.47	$187.45	$187.50
Purchase #2	$91.85	12.682%	$103.4984	$103.50	$103.50	$103.50
Purchase #3	$249.26	12.324%	$279.9788	$279.98	$280.00	$280.00
Purchase #4	$70.92	9.531%	$77.6794	$77.68	$77.70	$77.70
Purchase #5	$57.48	11.760%	$64.2396	$64.24	$64.25	$64.20
Purchase #6	$186.65	3.105%	$192.4455	$192.45	$192.45	$192.40
Purchase #7	$78.54	4.532%	$82.0994	$82.10	$82.10	$82.10
7 purchase totals =	$914.01		$987.4079	$987.42	$987.45	$987.40