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	$123.54	6.613%	$131.7097	$131.71	$131.70	$131.70
Purchase #2	$55.90	9.786%	$61.3704	$61.37	$61.35	$61.40
Purchase #3	$68.80	5.527%	$72.6026	$72.60	$72.60	$72.60
Purchase #4	$201.97	9.706%	$221.5732	$221.57	$221.55	$221.60
Purchase #5	$41.69	4.429%	$43.5365	$43.54	$43.55	$43.50
Purchase #6	$152.68	13.171%	$172.7895	$172.79	$172.80	$172.80
Purchase #7	$144.85	13.664%	$164.6423	$164.64	$164.65	$164.60
7 purchase totals =	$789.43		$868.2242	$868.22	$868.20	$868.20