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	$88.93	12.615%	$100.1485	$100.15	$100.15	$100.10
Purchase #2	$147.32	3.130%	$151.9311	$151.93	$151.95	$151.90
Purchase #3	$234.59	8.172%	$253.7607	$253.76	$253.75	$253.80
Purchase #4	$5.68	10.237%	$6.2615	$6.26	$6.25	$6.30
Purchase #5	$160.30	7.811%	$172.821	$172.82	$172.80	$172.80
Purchase #6	$101.76	11.603%	$113.5672	$113.57	$113.55	$113.60
Purchase #7	$62.67	10.824%	$69.4534	$69.45	$69.45	$69.50
7 purchase totals =	$801.25		$867.9434	$867.94	$867.90	$868.00