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	$33.98	12.485%	$38.2224	$38.22	$38.20	$38.20
Purchase #2	$142.63	9.679%	$156.4352	$156.44	$156.45	$156.40
Purchase #3	$215.31	12.406%	$242.0214	$242.02	$242.00	$242.00
Purchase #4	$106.61	4.867%	$111.7987	$111.80	$111.80	$111.80
Purchase #5	$196.60	3.536%	$203.5518	$203.55	$203.55	$203.60
Purchase #6	$103.43	13.823%	$117.7271	$117.73	$117.75	$117.70
Purchase #7	$147.25	3.166%	$151.9119	$151.91	$151.90	$151.90
7 purchase totals =	$945.81		$1,021.6685	$1,021.67	$1,021.65	$1,021.60