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	$166.34	13.802%	$189.2982	$189.30	$189.30	$189.30
Purchase #2	$112.32	10.422%	$124.026	$124.03	$124.05	$124.00
Purchase #3	$57.76	6.304%	$61.4012	$61.40	$61.40	$61.40
Purchase #4	$87.46	3.326%	$90.3689	$90.37	$90.35	$90.40
Purchase #5	$54.96	12.845%	$62.0196	$62.02	$62.00	$62.00
Purchase #6	$14.75	10.633%	$16.3184	$16.32	$16.30	$16.30
Purchase #7	$52.34	7.874%	$56.4613	$56.46	$56.45	$56.50
7 purchase totals =	$545.93		$599.8936	$599.90	$599.85	$599.90