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	$112.74	9.654%	$123.6239	$123.62	$123.60	$123.60
Purchase #2	$189.25	7.309%	$203.0823	$203.08	$203.10	$203.10
Purchase #3	$29.96	8.356%	$32.4635	$32.46	$32.45	$32.50
Purchase #4	$115.65	6.724%	$123.4263	$123.43	$123.45	$123.40
Purchase #5	$109.50	3.599%	$113.4409	$113.44	$113.45	$113.40
Purchase #6	$153.83	8.496%	$166.8994	$166.90	$166.90	$166.90
Purchase #7	$113.42	9.711%	$124.4342	$124.43	$124.45	$124.40
7 purchase totals =	$824.35		$887.3705	$887.36	$887.40	$887.30