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	$68.98	4.429%	$72.0351	$72.04	$72.05	$72.00
Purchase #2	$162.55	5.141%	$170.9067	$170.91	$170.90	$170.90
Purchase #3	$159.96	9.285%	$174.8123	$174.81	$174.80	$174.80
Purchase #4	$132.69	13.397%	$150.4665	$150.47	$150.45	$150.50
Purchase #5	$80.68	9.184%	$88.0897	$88.09	$88.10	$88.10
Purchase #6	$205.34	9.753%	$225.3668	$225.37	$225.35	$225.40
Purchase #7	$46.44	8.255%	$50.2736	$50.27	$50.25	$50.30
7 purchase totals =	$856.64		$931.9507	$931.96	$931.90	$932.00