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	$129.84	11.370%	$144.6028	$144.60	$144.60	$144.60
Purchase #2	$142.38	9.684%	$156.1681	$156.17	$156.15	$156.20
Purchase #3	$63.70	13.340%	$72.1976	$72.20	$72.20	$72.20
Purchase #4	$110.45	5.435%	$116.453	$116.45	$116.45	$116.50
Purchase #5	$243.43	13.813%	$277.055	$277.06	$277.05	$277.10
Purchase #6	$242.38	5.227%	$255.0492	$255.05	$255.05	$255.00
Purchase #7	$112.39	5.279%	$118.3231	$118.32	$118.30	$118.30
7 purchase totals =	$1,044.57		$1,139.8488	$1,139.85	$1,139.80	$1,139.90