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	$69.76	11.172%	$77.5536	$77.55	$77.55	$77.60
Purchase #2	$105.44	12.307%	$118.4165	$118.42	$118.40	$118.40
Purchase #3	$135.65	9.557%	$148.6141	$148.61	$148.60	$148.60
Purchase #4	$168.80	4.494%	$176.3859	$176.39	$176.40	$176.40
Purchase #5	$98.94	10.334%	$109.1645	$109.16	$109.15	$109.20
Purchase #6	$237.50	7.572%	$255.4835	$255.48	$255.50	$255.50
Purchase #7	$109.55	8.477%	$118.8366	$118.84	$118.85	$118.80
7 purchase totals =	$925.64		$1,004.4547	$1,004.45	$1,004.45	$1,004.50