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	$235.91	8.314%	$255.5236	$255.52	$255.50	$255.50
Purchase #2	$98.84	3.807%	$102.6028	$102.60	$102.60	$102.60
Purchase #3	$244.59	10.328%	$269.8513	$269.85	$269.85	$269.90
Purchase #4	$123.91	13.426%	$140.5462	$140.55	$140.55	$140.50
Purchase #5	$241.44	5.547%	$254.8327	$254.83	$254.85	$254.80
Purchase #6	$56.32	6.806%	$60.1531	$60.15	$60.15	$60.20
Purchase #7	$131.39	7.794%	$141.6305	$141.63	$141.65	$141.60
7 purchase totals =	$1,132.40		$1,225.1402	$1,225.13	$1,225.15	$1,225.10