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	$172.69	11.401%	$192.3784	$192.38	$192.40	$192.40
Purchase #2	$134.39	6.812%	$143.5446	$143.54	$143.55	$143.50
Purchase #3	$226.74	12.643%	$255.4067	$255.41	$255.40	$255.40
Purchase #4	$121.37	7.785%	$130.8187	$130.82	$130.80	$130.80
Purchase #5	$36.64	6.442%	$39.0003	$39.00	$39.00	$39.00
Purchase #6	$149.31	11.794%	$166.9196	$166.92	$166.90	$166.90
Purchase #7	$37.52	3.458%	$38.8174	$38.82	$38.80	$38.80
7 purchase totals =	$878.66		$966.8857	$966.89	$966.85	$966.80