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	$21.33	4.328%	$22.2532	$22.25	$22.25	$22.30
Purchase #2	$196.51	10.827%	$217.7861	$217.79	$217.80	$217.80
Purchase #3	$32.71	9.159%	$35.7059	$35.71	$35.70	$35.70
Purchase #4	$172.45	13.151%	$195.1289	$195.13	$195.15	$195.10
Purchase #5	$101.46	9.464%	$111.0622	$111.06	$111.05	$111.10
Purchase #6	$225.93	5.264%	$237.823	$237.82	$237.80	$237.80
Purchase #7	$143.36	9.414%	$156.8559	$156.86	$156.85	$156.90
7 purchase totals =	$893.75		$976.6152	$976.62	$976.60	$976.70