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	$144.84	11.370%	$161.3083	$161.31	$161.30	$161.30
Purchase #2	$19.51	9.661%	$21.3949	$21.39	$21.40	$21.40
Purchase #3	$211.52	3.600%	$219.1347	$219.13	$219.15	$219.10
Purchase #4	$219.96	12.677%	$247.8443	$247.84	$247.85	$247.80
Purchase #5	$243.31	5.817%	$257.4633	$257.46	$257.45	$257.50
Purchase #6	$169.31	12.863%	$191.0883	$191.09	$191.10	$191.10
Purchase #7	$40.61	11.334%	$45.2127	$45.21	$45.20	$45.20
7 purchase totals =	$1,049.06		$1,143.4465	$1,143.43	$1,143.45	$1,143.40