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	$39.45	7.330%	$42.3417	$42.34	$42.35	$42.30
Purchase #2	$166.73	8.503%	$180.9071	$180.91	$180.90	$180.90
Purchase #3	$113.39	7.109%	$121.4509	$121.45	$121.45	$121.50
Purchase #4	$173.63	7.555%	$186.7477	$186.75	$186.75	$186.70
Purchase #5	$127.72	11.471%	$142.3708	$142.37	$142.35	$142.40
Purchase #6	$132.77	3.373%	$137.2483	$137.25	$137.25	$137.20
Purchase #7	$96.81	7.350%	$103.9255	$103.93	$103.95	$103.90
7 purchase totals =	$850.50		$914.9920	$915.00	$915.00	$914.90