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	$189.28	12.722%	$213.3602	$213.36	$213.35	$213.40
Purchase #2	$56.26	5.320%	$59.253	$59.25	$59.25	$59.30
Purchase #3	$125.64	5.746%	$132.8593	$132.86	$132.85	$132.90
Purchase #4	$39.55	6.570%	$42.1484	$42.15	$42.15	$42.10
Purchase #5	$150.59	10.269%	$166.0541	$166.05	$166.05	$166.10
Purchase #6	$106.72	13.357%	$120.9746	$120.97	$120.95	$121.00
Purchase #7	$104.60	11.302%	$116.4219	$116.42	$116.40	$116.40
7 purchase totals =	$772.64		$851.0715	$851.06	$851.00	$851.20