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	$71.72	9.512%	$78.542	$78.54	$78.55	$78.50
Purchase #2	$243.40	3.772%	$252.581	$252.58	$252.60	$252.60
Purchase #3	$20.47	8.209%	$22.1504	$22.15	$22.15	$22.20
Purchase #4	$6.39	4.334%	$6.6669	$6.67	$6.65	$6.70
Purchase #5	$96.49	4.131%	$100.476	$100.48	$100.50	$100.50
Purchase #6	$192.44	3.691%	$199.543	$199.54	$199.55	$199.50
Purchase #7	$125.46	4.784%	$131.462	$131.46	$131.45	$131.50
7 purchase totals =	$756.37		$791.4213	$791.42	$791.45	$791.50