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	$33.70	4.257%	$35.1346	$35.13	$35.15	$35.10
Purchase #2	$199.75	5.526%	$210.7882	$210.79	$210.80	$210.80
Purchase #3	$247.88	6.395%	$263.7319	$263.73	$263.75	$263.70
Purchase #4	$107.83	3.252%	$111.3366	$111.34	$111.35	$111.30
Purchase #5	$37.25	8.623%	$40.4621	$40.46	$40.45	$40.50
Purchase #6	$176.64	4.651%	$184.8555	$184.86	$184.85	$184.90
Purchase #7	$83.32	12.570%	$93.7933	$93.79	$93.80	$93.80
7 purchase totals =	$886.37		$940.1022	$940.10	$940.15	$940.10