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	$180.56	5.162%	$189.8805	$189.88	$189.90	$189.90
Purchase #2	$158.52	11.404%	$176.5976	$176.60	$176.60	$176.60
Purchase #3	$174.26	6.198%	$185.0606	$185.06	$185.05	$185.10
Purchase #4	$244.69	5.794%	$258.8673	$258.87	$258.85	$258.90
Purchase #5	$250.37	3.289%	$258.6047	$258.60	$258.60	$258.60
Purchase #6	$180.56	4.336%	$188.3891	$188.39	$188.40	$188.40
Purchase #7	$6.78	4.114%	$7.0589	$7.06	$7.05	$7.10
7 purchase totals =	$1,195.74		$1,264.4587	$1,264.46	$1,264.45	$1,264.60