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	$130.47	10.254%	$143.8484	$143.85	$143.85	$143.80
Purchase #2	$54.28	11.455%	$60.4978	$60.50	$60.50	$60.50
Purchase #3	$195.51	11.808%	$218.5958	$218.60	$218.60	$218.60
Purchase #4	$135.26	4.584%	$141.4603	$141.46	$141.45	$141.50
Purchase #5	$83.94	7.716%	$90.4168	$90.42	$90.40	$90.40
Purchase #6	$78.49	8.171%	$84.9034	$84.90	$84.90	$84.90
Purchase #7	$45.54	9.406%	$49.8235	$49.82	$49.80	$49.80
7 purchase totals =	$723.49		$789.5460	$789.55	$789.50	$789.50