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	$21.61	4.416%	$22.5643	$22.56	$22.55	$22.60
Purchase #2	$198.37	6.786%	$211.8314	$211.83	$211.85	$211.80
Purchase #3	$69.56	12.522%	$78.2703	$78.27	$78.25	$78.30
Purchase #4	$56.69	4.209%	$59.0761	$59.08	$59.10	$59.10
Purchase #5	$70.83	13.843%	$80.635	$80.64	$80.65	$80.60
Purchase #6	$50.90	7.200%	$54.5648	$54.56	$54.55	$54.60
Purchase #7	$30.45	4.125%	$31.7061	$31.71	$31.70	$31.70
7 purchase totals =	$498.41		$538.6480	$538.65	$538.65	$538.70