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	$42.77	4.123%	$44.5334	$44.53	$44.55	$44.50
Purchase #2	$144.46	10.829%	$160.1036	$160.10	$160.10	$160.10
Purchase #3	$64.72	11.419%	$72.1104	$72.11	$72.10	$72.10
Purchase #4	$221.77	4.319%	$231.3482	$231.35	$231.35	$231.30
Purchase #5	$118.39	8.581%	$128.549	$128.55	$128.55	$128.50
Purchase #6	$220.86	3.348%	$228.2544	$228.25	$228.25	$228.30
Purchase #7	$92.43	7.202%	$99.0868	$99.09	$99.10	$99.10
7 purchase totals =	$905.40		$963.9858	$963.98	$964.00	$963.90