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	$138.63	5.588%	$146.3766	$146.38	$146.40	$146.40
Purchase #2	$176.72	5.179%	$185.8723	$185.87	$185.85	$185.90
Purchase #3	$175.83	4.404%	$183.5736	$183.57	$183.55	$183.60
Purchase #4	$41.37	5.180%	$43.513	$43.51	$43.50	$43.50
Purchase #5	$46.68	7.333%	$50.103	$50.10	$50.10	$50.10
Purchase #6	$59.42	8.513%	$64.4784	$64.48	$64.50	$64.50
Purchase #7	$215.85	10.548%	$238.6179	$238.62	$238.60	$238.60
7 purchase totals =	$854.50		$912.5348	$912.53	$912.50	$912.60