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	$176.53	4.851%	$185.0935	$185.09	$185.10	$185.10
Purchase #2	$123.96	9.745%	$136.0399	$136.04	$136.05	$136.00
Purchase #3	$104.96	3.417%	$108.5465	$108.55	$108.55	$108.50
Purchase #4	$151.63	13.248%	$171.7179	$171.72	$171.70	$171.70
Purchase #5	$127.62	13.218%	$144.4888	$144.49	$144.50	$144.50
Purchase #6	$208.88	8.464%	$226.5596	$226.56	$226.55	$226.60
Purchase #7	$66.87	5.243%	$70.376	$70.38	$70.40	$70.40
7 purchase totals =	$960.45		$1,042.8222	$1,042.83	$1,042.85	$1,042.80