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	$207.88	6.481%	$221.3527	$221.35	$221.35	$221.40
Purchase #2	$217.96	3.410%	$225.3924	$225.39	$225.40	$225.40
Purchase #3	$99.25	6.242%	$105.4452	$105.45	$105.45	$105.40
Purchase #4	$133.29	8.136%	$144.1345	$144.13	$144.15	$144.10
Purchase #5	$41.59	8.243%	$45.0183	$45.02	$45.00	$45.00
Purchase #6	$236.75	3.803%	$245.7536	$245.75	$245.75	$245.80
Purchase #7	$145.68	4.657%	$152.4643	$152.46	$152.45	$152.50
7 purchase totals =	$1,082.40		$1,139.5610	$1,139.55	$1,139.55	$1,139.60