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	$91.49	9.479%	$100.1623	$100.16	$100.15	$100.20
Purchase #2	$136.62	10.215%	$150.5757	$150.58	$150.60	$150.60
Purchase #3	$112.56	6.854%	$120.2749	$120.27	$120.25	$120.30
Purchase #4	$44.70	13.352%	$50.6683	$50.67	$50.65	$50.70
Purchase #5	$136.76	8.856%	$148.8715	$148.87	$148.85	$148.90
Purchase #6	$19.37	12.837%	$21.8565	$21.86	$21.85	$21.90
Purchase #7	$225.78	8.541%	$245.0639	$245.06	$245.05	$245.10
7 purchase totals =	$767.28		$837.4731	$837.47	$837.40	$837.70