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	$42.50	3.232%	$43.8736	$43.87	$43.85	$43.90
Purchase #2	$217.94	9.743%	$239.1739	$239.17	$239.15	$239.20
Purchase #3	$203.80	6.284%	$216.6068	$216.61	$216.60	$216.60
Purchase #4	$144.42	5.682%	$152.6259	$152.63	$152.65	$152.60
Purchase #5	$76.50	13.642%	$86.9361	$86.94	$86.95	$86.90
Purchase #6	$128.72	8.687%	$139.9019	$139.90	$139.90	$139.90
Purchase #7	$54.29	12.549%	$61.1029	$61.10	$61.10	$61.10
7 purchase totals =	$868.17		$940.2211	$940.22	$940.20	$940.20